Ihave a 2001 chevy Z71 the automatic transmission is makeing me nerveous. It wont go into the tow haul mode. At about 55mph the transmission acts like it cant decide whether it wants to be in 3rd or 4th gear. Run it up to about 60 to 65 mph and it runs fine. It seems to shift fine other than that. Does however seem to shift slow when its cold. Have heard it might be a vehicle speed sensor. hope you guys can help not ready to put in a tranny. thanks for the help.

 

If it was a sensor i would think it would be a crankshaft positioning sensor make sure it has enough ATF and that what it does have isnt burnt or black.