I have a major trans problem.. I have no clue what it is. Ok first the trans set up. th350 reverse manual valve body. Here's the problem.. Take off in first gear all good.. hit second all good till i lift off the gas.. back tires lock up and send the car sideways down the street... don't unlock till i can get it into nutral. Hapens whenever i let off the gas and sometimes when still on the gas lightly.. Any help would be great.

 

now i found something else wierd about it.. If you go from revers to 1 it will not engage first.. but if you turn the car off at that point and re-start it, its in first gear ready to go.. Also when it locks the back tires up and stops.. if you put it back in frist it goes backwards... what the heck is wrong with this thing.. Should i just get a diffent valve body put in it?