My 88 GMC 3500, 454Tbi, 400TH auto tranny is giving me yet another problem. When I crank it up and put it in reverse it shifts really really hard, hard enough you can hear the drive shaft clank. It acts as if it is revved up why too high, and will almost squeal tires if I dont have my foot on the brake all the way when I first put it into reverse. When I put in drive its idels just fine. I have replaced the transmission modulator, checked the vacum line, check the transmission fluid and all seems to be fine. This transmission was rebuilt by one of the best shops in town less than a year ago. Also, while driving down the road under no harsh load, it will take forever to change from 2nd to 3rd, I have to let my foot off the gas pedal and it will change, and sometimes I just have to give it even more gas to make it shift and when it does its a very hard shift. Any ideas? So far in the past 4 months I have put a new exhaust on it, replaced alternator, clutch fan, plugs wires, radiator, starter, tires, and hopefully not a transmission. My plans are to get this hard shifting problem fixed and sell this bad boy. There is a 96 GMC sonoma 4.3 Vortec that my father in law has he wants me to buy from him. I gotta admit, the gas would be better.