Lucky for us, Asin also sold this transmission to JEEP, and they used in on the Cherokee....
So, go to any JEEP dealer, and talk to the service department. They have all the tools needed (or should have) to rebuild this tranmission. My rebuilt R154 used Mopar shift forks.. (Well, the bags were marked Mopar, but the forks had the Asin logo's cast into them...)
Parts are generally less money too compared to Toyota, which is why mine are "Mopar" LOL
I know this same transmission is now being used in the midsized Chevy truck as well, so the Chevy dealer/service might have the parts and tools to do the work.
That being said, my trans rebuild was only about 700.00, and I replaced second gear, all new synchro rings, bearings and thrust washers. I think the parts were about 200.00 because of the gear, the bearings and other parts were bought as a kit from Mopar for the Cherokee transmisison.
One thing I did while this trans was torn down was themal coat the cases, moly coat the shift fork pads and other wear surfaces, debur and moly coat the thrust washer and moly coat the rear bushing as well. Now the entire transmission case acts like a huge surface cooler, and the suspect first gear thrust washer should never be a problem.
The trans runs much cooler than it used to. On long trips, in the summer, or even in cooler weather, the shifter would be very hot after a few hours of driving. Now it just get's luke warm, even on the hottest days when it used to get so hot it was painfull to touch, it's now just slightly warm.
Be ready for a difficult to shift first 500 miles however. This thing was tight when it was done, and has only gotten better as it's broken in.