My'99 3/4 ton, four door, 350, 95k miles, old body style has begun shifting hard on the upshift. It shifts hard, as though a shift kit was installed. Normally they mesh very smooth. I drained the tranny, installed new filter and gasket with no abnormal metal filings on the magnetic drain plug. Problem went away. 2 months later same problem.It is intermittant to some extent.I rarelydo any towing and never use overdrive when doing so. I was told that model hadtwodifferent transmissions installed. I believemine has the 19 bolt pan if it makes any difference. Any suggestions?

Thanks in advance.

 

You may have some part of the valve body sticking until it build up enough pressure to break loose, causing it to act like it has a shift kit. I would try calling a good tranny shop and tell them the same thing and see what they say.

 

AM HAVING SAME PROBLEM OUT OF MY *97 TAHOE, TRANNY IS A 4L60E AND HAVE BEEN TOLD BY SEVERAL SHOPS SAME THING, VALVE , OR COULD POSSIBLY BE A SHIFT SOLENOID, IT WILL ALSO STOP DOING IT IF YOU CYCLE YOUR KEY OFF AND BACK ON, AND DRIVE IN 3RD UNTILL FIXED.
IF YOU WISH TO TACKLE IT YOURSELF GO TO P&S TRANSMISSION PARTS ONLINE THEY HAVE A KIT THAT WILL HELP YOU, ALSO PRO-BUILT AUTOMATICS HAS AN ONLINE STORE THAT DETAILS INSTRUCTIONS AS TO WHAT TO DO. HOPE TO BE OF HELP , AM FIXING TO DO SAME WORK ON MINE.
TY, LIL