1996 Chevy Tahoe Transmission Trouble

[USoccerT]

I own a 96' Tahoe that currently has 124,000 miles on it. Exacly one year and two weeks ago I was driving across Texas and after driving at Highway speeds for an hour or two had to come to a stop entering a small town. When starting up from the dead stop the engine made a horrible grinding sound which continued and worsened at the vehicle accelerated and dissapeared entierly when it shifted into second. The transmission was also silent in third and in fourth/ overdrive until 75 mph or so. The sound was also present in reverse gear. The vehicle slowly limped home, using only drive gears 2 & 3. I prceeded to gather info from mechanics and othe knowedgables about what might have gone wrong, after all the average live of a transmission in this type of vehicle was around 115k-120k, basically what I got out of it. The best determination was that the first gear planet, used in 1st, overdrive, and reverse, had given out or lost it's inner bushing, causing it to wobble around the shaft and grinding against everything. Eventually I ordered a fully rebuilt transmission from Phoenix Hard Parts online, reasonably priced, and installed it myself, literally. The transmission came with a new torque converter and I also purchased a new transmission cooler and took great care to blow out the cooling lines with 125psi compressed air. The transmission seemed to work normal until yesterday morning I headed off to work and the same horrible grinding sound came out of the transmission as I drove off. I am now pretty certain that it must have been an electrical problem that caused the previous transmission to fail. I don't want to pay $2500-$300 plus to get this fixed if I can still do the work myself. Is there anyway for me to test the various electrical components that feed the transmission information to see if that was the cause before I buy another re-built transmission and only get 7500 miles out of it? Would it be easier and cheaper to just switch the vehicle to a manual transmission? Do they make a manual transmission that would work for my vehicle, I don't mind stipping the 4X4 ability, I just want to be able to drive it. The transmission is a type 4L60E with a 2000 stall torque converter. There are no current fault codes shown on the computer, and I drive like an old lady, so I know I didn't rag it out. Any help would be greatly appreciated. Thanks for taking the time to read my incredibly long post.