I have a 2000 GMC with 5.7 engine & 4L80E transmission. Truck has 121000
miles, but it appears that the transmission and TC have been changed. I
have had the truck about 14 months and it was done sometime before I got it.
TC is coming unlocked and it is dropping back to 3rd gear. Can pull off to
the side of road , turn off switch and give it about 30 seconds, restart and
it does fine.Then it may go 30 miles or it might go 130 before it does it
again. Doesn't seem to be a connection to how hot the fluid may be.It
always happens between 50 & 60 MPH and when you are only slightly pulling.
(Service Engine Soon) light has never come on. It is throwing a 1870 code
I have changed the fluid and filter and it looked good. Nothing in the
filter or pan and the fluid looked and smelled like it had just come out of
the bottle. The front of TC did not have any sign of hot spots on it.
I'm no mechanic, but I think it is an elec. problem, but don't know how to
trace it down.
Anyone have any ideas?