Best manual transmission fluid for the NV3550?

Tried both. First Royal Purple, then MTL. Then I went back to RP when it was time.

2003 Rubicon
 
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Tried both. First Royal Purple, then MTL. Then I went back to RP when it was time.

2003 Rubicon

Same here, did RP back in 2015 and put in Red Line MTL last weekend. What came out was black, so after 2.5 years that RP was all done.

I also did the transfer case, same time period, and that RP fluid was still good, didn't need to change it.

Time will tell if Red Line MTL performs better, but shifting is much better now, but very similar to 2015 when I put RP in there.
 
I've been using Redline MTL since well before my introduction to TJ's, started off in my Triumph TR6 about 15 years ago and have been using it since. After picking up my current Wrangler with the AX5 I did a clutch replacement and fluid change and the improvement to the trans was remarkable.
 
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I'm no fan of Royal Purple. My belief is it's an overpriced lube that is no better than anything else. It just also includes a short-lived purple dye added to it for marketing purposes. If it were me, I'd go with Redline who doesn't feel the need to add a dye to make people buy it.
 
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I'm no fan of Royal Purple. My belief is it's an overpriced lube that is no better than anything else. It just also includes a short-lived purple dye added to it for marketing purposes. If it were me, I'd go with Redline who doesn't feel the need to add a dye to make people buy it.

Why do you feel that RP is overpriced? The oil is priced where Mobil, Castrol, Pennzoil, Valvoline are priced. I do not have enough knowledge on each brands secret formula, but just curious to know if your dislike towards RP is due to the purple dye, or if they are on par with low end oil but selling at premium prices?

It's a tough market to enter when you have established brands like Mobil and Castrol, so adding a meaningless dye for marketing purposes doesn't matter to me, as long as it doesn't harm my vehicle and I am overpaying for snake oil.

Personally I did use RP but have moved on to Red Line and Amsoil as my go to oils....with the exception of engine oil which I get the best priced name brand from Advanced Auto.
 
Personally, I would just use Mopar fluid (part #04874464AA) or Synchromax.
I definitely would not use Synchromesh from Pennzoil or GM. That particular lube has too many complaints about how the transmission shifts and behaves after filling the transmission with it. It meets the specs but it sure doesn't have many who like how it works once they use it. Not to mention it is a conventional gear lube which during super cold conditions can cause shifting issues.
 
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I have used Redline MTL and then Royal Purple Synchomax and can virtually tell no difference in performance between the two. When I changed to the Redline from the factory oil, I immediately could tell smoother shifting, especially when cold. Noise level was about the same for a box of rocks that is the NV3550. Had I switched to RP from the factory oil first, I probably would have praised the RP as a performance enhancement, but the Redline netted the same results as the RP.
Pricing is all over the place on this stuff. two examples would lead you to believe that the RP is less expensive.

https://www.summitracing.com/parts/...MI15e2tozv2QIVlGp-Ch0YGg80EAQYASABEgKZm_D_BwE

https://www.summitracing.com/parts/...MItuXM-4zv2QIVlZN-Ch3qdAJ_EAQYASABEgLvO_D_BwE

However, I called my local Napa Auto and I can get Redline MTL for $12.49 qt. vs. Royal Purple Synchomax at $18.71 qt. That there is a significant difference in cost between the two.
 
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I try to change the fluids while everything is still warm. Seems like ithey drain faster and more thoroughly.

2003 Rubicon