I have a 1999 blazer LT with 113k currently I bought it with 105k from a friend who bought it with 72k. I believe t he fluid was changed last around 85k but not sure. The trans shifts fine but I noticed when I drive to work (38 miles) once I get off the highway and come to a complete stop and proceed on from a stop it shifts hard from 1st to 2nd..some days it doesn't happen. I installed a snow plow and when I was plowing for the first time with it I noticed it was kinda grinding a little especially in reverse. I def gave it a workout plowing for 8 hrs strong.Would it be bad To change the fluid and filter or should I just leave it alone ??? Thank you

 

You mean 4.3 in your topic title..
And it would not hurt it to do a fluid change (in the pan) and a filter change.
Someone else will come in here and help on if the problem is bigger than that.

 

Should I avoid a flush and just get it drained and filled ??

 

i would avoid the flush just drop the pan change filter and oil maybe add some lucas transmission

 

The first thing to do is check for codes and fluid level when warm. Is it slipping in lockup at all? A hard 1-2 shift can be caused by a high tranny fluid temp. Do other gears shift hard? If so then it may be a TPS issue.

A fluid change can't hurt, its getting about due anyway.

 

Just do a filter pan change. subtract a quart and had a quart of lucas trans slip. Great stuff.

 

If I were to drive it around town for awhile it shifts very well but if I get on the highway (1/2 mile from home) and drive 38 miles at 75 mph exit the highway to a complete stop continue it slips pretty hard 75% of the time from 1st to 2nd, forgot to mention I already added a half bottle of Lucas a cople thousand miles ago. Awhile back I did get a code for something to do with the trans valve body but I just ignored it.

 

then there you go. Something internally is either dirty/sticking or bad. maybe a shift valve. Time to dig in.

 

First...get your codes.
Its not hard to pull the pan and check the solenoids or have it done.
The pan will be off anyway to change the filter.
Do it now before it costs you $2-3k!!

 

my 92 is shifting hard from 1st to 2nd (auto). just started a couple days ago when we had a warm day (Iowa). If I feather it, rpms hit about 2500 - 3k, then it shifts hard...but if I get on it, the shift is quick and not as hard.

Was told to replace the filter and fluid....now if i can find the time...