Redline MTL, Amsoil MTF, Torco MTF, Pennzoil/Texaco Synchromesh, RoyalPurple SynchroMax,..... are all options to consider. Thicker ATFs, like racing or hightemp ATF, can also be used. Pennzoil highmileage ATF, Redline Racing ATF, as well as ANY normal synthetic ATF, can also be tried.
Some manuals are pretty picky with shift quality, especially when cold. A couple of the above might be a little thicker then required. Since your location is in Texas, I don't expect issues.
Some manual transmissions are designed for ATF. Their load pattern, gear design, gear strength, are all taken into consideration when spec'ing a fluid. Thinner fluids lead to easier shifts for the wimpy consumer. And, thinner fluids lead to better MPG for the enviromentalists.
Don't go too thick. Some lubrication channels don't tolerate the reduced flow of thicker oils. I would NOT use a 90wt in a manual requiring ATF.
The recipe for long lasting manuals is quality fluids with a reasonable change interval. I prefer <30k change intervals depending on transmission and usage.