There shouldn't be so long as the coax cable you purchased shows markings on the side to the effect that it is 50 ohm impedance for that coax. I'd also say that you should run as short of a coax length as possible. 18 feet seems a bit excessive for the tj, but if that's what it takes, that's what it takes.
If you wanted to upgrade, there are lower loss coax cables available from reputable ham and CB vendors
Cable selection is based on several criteria: Characteristic impedance, which should be 50 ohms for CB, GMRS, and Ham. Cost - you usually get what you pay for. Shielding - this is the metal cover over the dielectric. More shielding means less interference.
Couple of other things to look at - all coax has a minimum bending radius; if you bend it too tight you will collapse the dielectric and cause a change in impedance which usually results in energy reflections back into your transmitter (bad). Connectors - make sure you can either a) install the cable and connectors for your application or b) buy extra connectors, solder, etc. Screw on connectors are usually not suitable. If you don't know how to solder (not solder plumbing!) elex, just go to a CB or Ham shop and pay to have it installed. Why spend several hundred dollars for gear and several hours of installation time, then go cheap on the cable?
Here is what I would use: https://www.amazon.com/dp/B001JT1IWU/?tag=wranglerorg-20
So, I ordered 9' of RG-58 coax, but received 9' of RG-8X. From what I've read, it's a little bit better, with lower loss, and is not much thicker (if at all) than my other RG-58 that I used for the CB. I'll just consider it a free upgrade unless anyone has a reason to recommend that I return it.