We have now had my son's 1999 Blazer ZR2 for around 6 months . It was bought with 114000 miles on it. We changed the auto trans fluid and filter right after we bought it. Installed Mobil #1 syn ATF. He has now put around 3,000 miles on it. Problem: After driving on the interstate for sometime, and pulling off, and then taking off again in town... the trans is shifting very hard from 1st to 2nd gear. Almost banging into 2nd gear. If you take off in the morning and stay around town, it so far does not do it. We had the check engine light come on when we 1st bought it, but it went out shortly after. Well it is now back on after a long 200 mile drive we took to see KISS in DC last month. The trans was banging into 2nd gear weeks before this. Does anyone have any idea what is the trouble? I read on the internet the the valve body wears out on this 4L60 trans and causes this to happen, and will need rebuilt. If it needs rebuilt, or another trans bought.... where do I get a upgraded trans that is better over stock? Thanks for all info....

 

Get the codes read and post them up so we can help with that.

You have read correctly about the 1-2 shift being related to a worn valve body. BUT, it could also be other worn parts inside the trans.

Have a look at this thread for more info:

Everyone having 1st to 2nd tranny slams HERE!.!.!

 

The hard shifting has stopped. The check engine light has also went off. I did not get a chance to have the code read. Working great now, but for how long? Trans guy at my local chevy dealer said it sounds like the valve body, but could be other things. My buddy said drive it tell it breaks!