The 8 speed is a nightmare…
The 8 speed is a nightmare. Almost all the trucks that come thru my shop are on their second or third trans or torque converter.
For anybody looking at that 8 speed market, do yourself a favor and get one with a bad transmission on the cheap. About half of them are chattering and slamming gears on the used market. Negotiate the deal and show the cost for a new trans. Get a new 8 speed trans. Have it tuned by a custom performance tuner to solve the torque converter issue. Keep it cool with the cooler mod. And you will have success. The problem with these 8 speeds is all due to GM keeping the truck fuel efficient as possible. The torque converter is constantly locking and unlocking. And slipping with each engagement. The new 10 speed transmissions stay locked and the issue is not present on the 10 speeds due to this. The 6 speeds will also benefit from taking it to a custom tuner and having the converter lock in only 5th and 6th gear.