between 35 and 42 mph the tach jumps and the car jerks does not do it at any other speed drives me crazy. Why

 

Yours is an auto, isn't it?

 

It would help to have some circumstances and specs.

Recent tun-up, bad weather, etc?

 

On my 06 2.2 automatic transmission, it will shift from 3rd to 4th gear usually between 37 and 40 MPH, depending on how much acceleration I am applying (if it's floored, the MPH is much higher, of course). This is quite smooth on mine, but seems like the likely culprit on yours. As long as you don't hear any bad noises or feel any severe jerking, you're probably OK, but you may want to take it to a service department for an inspection and tuneup, just to make sure nothing's wrong with it.

 

yes auto I think it may be the torque converter locking up

 

no tune up yet only 50,000 miles dry roads no unusual circumstances torque converter locking up is that covered underpowertrain warr.?

 

This problem seems to me more likely a transmission issue rather than a miss (as in misfire).

The torque converter clutch is part of the powertrain and is covered under your powertrain warranty. I'd take the car into your Chevrolet dealer, have them road test it and, if they can duplicate the symptom, request that it be repaired under warranty.

 

Sounds like a delay in the shift pattern allowing the rpms to increase before the next gear is fully engaged.....lock up converter does not cause this,it comes in after the shift is complete and the only indication will be a drop in rpms....a rise indicates a neutral condition.

 

going to the shop this week hope these idiots can figure it out

 

is powertrain warrenty 100.000 mjles