I'm brand new to this. Forgive me if this has already been addressed. I have looked through a lot of good information here. I have a 94 gmc sierra 4.3 liter with the 4L60e transmisssion. I paid some one to work on my truck a while back, they hooked up my shift linkage incorrectly. I was going down interstate when shifter jumped (by itself) from OD to reverse while doing 75mph. I had the transmisssion replaced. Now, when going down interstate doing 75mph with cruise control set, it jumps out of overdrive and my rpm's start racing higher. I am some what mechanically inclined however, I have never had to work on transmissions before.Please help