I have a 1996 chevy z71 truck with a 4l60e transmission the transmission is in limp home mode it seems to work fine when i first drive it but when it warms up it takes off in 3rd gear i check the fluid fuses under the hood hook a scaner to it no transmission codes i can manuly shift throught all the gears with the scaner and they work fine i check the wireing to the trans and it looks good and the wireing going to the pcm i just put a used pcm from the junk yard i bought this truck a week ago and it didnt run when i bought it and now i got it running good and the trans is in limp mode someone please help me thanks