1997 chev blazer full size,

so everythings fine driving, but it shifts into the last gear around 40 to 45mph,

then the truck jerks a little and the tach bounces not much, just a little. But when i push on the gas it runs fine, when i get it up to about 60 no bouncing or jerking. No codes at all ever.

I was told a vacuum line but where? ive looked all over under the hood i can hear a nouse hard to explain. kinda like a leaky faucet, u can hear it better inside the truck. but stops as i push on the gas more. even when in idle.

wonder if anyone has any ideas at all?

THanks

 

OK so we figured the problem, everyone said it was a vacuum line, we searched and searched all vacuum lines were fine..

tranny fluid was full HOT even went through all the gears checked again same. so we decided what the hell, add another quart, still read full hot, took it for a spin, and its gone, don't do it no more! so it read full but we couldnt think of anything else to try, but it worked.