1999.5 (new body style) Z71 Tranny issues
 

driving about 75 MPH in OD today on hwy I got into the throttle and tranny downshifted to pass. I felt a "stumble" in tranny and immediately lost OD and the RPM was 1000 higher than before this issue. It seemed as though I was now in regular drive. When I ran into some stop and go traffic on hwy it became apparent that the trans is not shifting to higher gears like it was previous to this situation. (does go into higher gear but RPM goes much higher than used to)
Once I got home I intended to back into the driveway but realized I no longer have reverse, all other drive positions engage ok except as noted above that the shift pattern has changed. I checked the fluid, not low or missing. Is there an electronic shift module that possibly has gone bad that might cause these conditions or something else besides trans itself?

Trans has approx 183K on it, serviced as should be, never abused but pulls boat trailer and 4 wheelers frequently but <2000lbs

Just looking for ideas/your experience

For those interested in what this issue turned out to be - the Sun Shell stripped out causing lose of reverse, 2nd gear and/or overdrive. In shop being rebuilt now

Yea, that is a common problem with the chevy trucks.

Wow Interesting. Thanks for sharing your tranni issue. What transmission is it?

Tranny is the 4L60E - hooked to the 5.3 V8. I have to say it has been a reliable drivetrain until I hit the 185K mark.

I just replaced the engine in August with brand new GM factory 5.3 (not a reman) and now the tranny should be like new....so I expect another 180K plus out of it. LOL...

Well I'm glad it all worked out for you. Hope you can come back and hang out with us and possibly help others

My truck just hit 100,000, and i have about 92,000 left on the warranty, so I should be good to go.

I appreciate the replies to my post. I'll post a pic or two of the Sierra when I get it back from the shop. I have had it since 17K miles on it, Been a great vehicle, but as you know, anything mechanical is subject to breakage.

1999.5 GMC Sierra, extended cab Z71 w/manual shift xfer case, K&N air intake, stainless exhaust with nice low/moderate rumble, leveled suspension, matching color topper on bed, spray lined bed, tailgate and top rails.

Atleast when the reaction shell strips out you are not left in tennis shoe mode.

We lost ours in the driveway when going into reverse. It was a '99 S10 Blazer w/140K on it. I pulled the transmission, replaced the shell and affected gaskets and reassembled. Still going with 181K+.

Friend of mine waited one day to trade his '97 Z71 in and that one day is when the sun shell stripped out and cost him almost 2K off the trade.

Same thing happened to my dad.