My 1997 Jimmy has 307,000 on it, transmission and engined never opened except for fluid changes. For the last 100,000 miles on random occasions the check engine light will come on and the 1 to 2 shift will be a slammer, I mean BANG, twice I went to Autozone they read the code said it was the TPS (throttle position sensor) I replaced it twice and they seem to last awhile then Bang away we go again. Now let me explain it is random, if I don't change it, it goes away for awhile. When it comes back I manually shift, don't use first, until it heals itself.

Whats up?

 

My 98 was doing that usually after a long highway cruise. At the first set of lights the 1-2 shift was like major shift kit quality. I then noticed occasionally I had a bit of a tranny slip, usually noticeable moreso on cruise control, at highway speeds. The tranny goes into a limp mode if there is any slip in the tranny, and mine ended up puking on the highway and I had to have it rebuilt.
Maybe time for a rebuild? Tranny shop or good shop should see a code for tranny slip. Weird it would show a TPS code.

 

Yeah, I know weird.
Both times I changed the TPS it was good for quite a while.
Until recently I was driving it 1300 miles a week never felt anything bad at speed.
Right now working great, whatever eh?

 

That's so many miles...like Volvo many. That's intriguing, makes me want to go on a 200,000 mile road trip in my Blazer right now

 

You mayneed to have the valve body replaced in your transmission(if it's auto) what could be happening is the valve is sticking and then it just pops open letting tranny shift causing the kick/buck.

 

I have the same problem while shifting 1 st - 2 nd , it is not happening all time , Unfotunatly when I go to workshop it disappear.
if you are suggesting TPS can I see that part some where on the net

 

https://blazerforum.com/m_90884/tm.htm