Starting to get a bit frustrated with trouble-shooting so hoping maybe someone has come across a similar/same issue that may have a suggestion or two on anything else to test prior to opening up the wallet 
Purchased a 2005 TJ SE, 4.0 back in december via facebook marketplace and issues began the day I drove it home - all good on backroads but had some issues on the highway with the jeep randomly downshifting for no reason and sending the RPMs sky high. It was mostly an around-town Jeep and did not experience that again as I am not on the highway much. Few weeks later started having issues with it not shifting correctly, and in a couple instances would not drive at all. Next day Check Engine Light. Checked my fluids and realized that the Transmission Fluid dipstick was reading basically nothing (while in neutral), and there was also transmission fluid leak. Since then it's been stuck in Limp Mode and keeps throwing the same codes - P0700, P0891
Check engine lights for P0700 from what I understand just says "hey something is wrong" and the P0891 is "TCM Power Relay Sense Circuit High".
Thing's I've done, in case anything may be related:
-After bringing it home, but a few weeks before the CEL, added in a Speedohealer to adjust the speedometer reading. (i got it spot on, easy install, really impressed). I've disconnected it to help rule things out.
-removed the transmission oil pan, cleaned off the old paper gasket, resealed with ATV and refilled. About 6ish quarts drained out and refilled then topped accordingly (no leaks! at least a win there though might have have slightly overfilled and could remove some, other posts suggest it should be ok).
-battery tests at 12.8 V. Transmission fuse (#5 in the power distribution center [PDC]) is intact, 12.8 V coming to it, and when inserted, sends the 12,8v over to the transmission control relay which also tests OKAY.
-Can clear codes but they come back within driving 300 feet, and stuck in limp mode.
With the error being regarding the relay, and reading countless outlines of others with 05's having issues with the PCM I am starting to lean towards the possibility of it being PCM (and will 100% go with WranglerFix!). But in the back of my head I wonder "ok or did something go sideways with the transmission?" and wonder just because the timing is so coincidental to me and makes me scratch my head. Sure I could bring it to a shop, and pay a few hundred for diagnosing and maybe not even get solutions, OR, can go with a new PCM and hope that helps, and worst case is it doesnt solve the issue BUT I would still have a new PCM and will be back to troubleshooting.
Should I look to target a problem transmission? orrrr a problem PCM, and are are there any other diagnostics I can perform to try and narrow things down?
TIA!!!
Purchased a 2005 TJ SE, 4.0 back in december via facebook marketplace and issues began the day I drove it home - all good on backroads but had some issues on the highway with the jeep randomly downshifting for no reason and sending the RPMs sky high. It was mostly an around-town Jeep and did not experience that again as I am not on the highway much. Few weeks later started having issues with it not shifting correctly, and in a couple instances would not drive at all. Next day Check Engine Light. Checked my fluids and realized that the Transmission Fluid dipstick was reading basically nothing (while in neutral), and there was also transmission fluid leak. Since then it's been stuck in Limp Mode and keeps throwing the same codes - P0700, P0891
Check engine lights for P0700 from what I understand just says "hey something is wrong" and the P0891 is "TCM Power Relay Sense Circuit High".
Thing's I've done, in case anything may be related:
-After bringing it home, but a few weeks before the CEL, added in a Speedohealer to adjust the speedometer reading. (i got it spot on, easy install, really impressed). I've disconnected it to help rule things out.
-removed the transmission oil pan, cleaned off the old paper gasket, resealed with ATV and refilled. About 6ish quarts drained out and refilled then topped accordingly (no leaks! at least a win there though might have have slightly overfilled and could remove some, other posts suggest it should be ok).
-battery tests at 12.8 V. Transmission fuse (#5 in the power distribution center [PDC]) is intact, 12.8 V coming to it, and when inserted, sends the 12,8v over to the transmission control relay which also tests OKAY.
-Can clear codes but they come back within driving 300 feet, and stuck in limp mode.
With the error being regarding the relay, and reading countless outlines of others with 05's having issues with the PCM I am starting to lean towards the possibility of it being PCM (and will 100% go with WranglerFix!). But in the back of my head I wonder "ok or did something go sideways with the transmission?" and wonder just because the timing is so coincidental to me and makes me scratch my head. Sure I could bring it to a shop, and pay a few hundred for diagnosing and maybe not even get solutions, OR, can go with a new PCM and hope that helps, and worst case is it doesnt solve the issue BUT I would still have a new PCM and will be back to troubleshooting.
Should I look to target a problem transmission? orrrr a problem PCM, and are are there any other diagnostics I can perform to try and narrow things down?
TIA!!!