2017 Chevy Silverado Shudder problems 4.3L

[Ronald Carlson]

I have a 4.3L Chevy Silverado Truck 2017.  Bought new and after short time of having it started having shudder problems.  has been in garage numerous times and the last time they said they put a new torque pump in it.  Well the problem is still there.  It happens around 1250 RPM and between 35 and 45 MPH when you try to maintain that speed.  The dealer I bought it off of is out of business and the new dealer is the one that said they put the torque pump in.  The truck has only 28,000 mile on it.  I called the garage and told them the problem is still there!  They said to bring the truck back in on Dec. 13, 2019 they said to drop it off early morning and they would check it out.  I told them the speed it does it and the RPM it does it.  Truck was dropped off at 7:45 AM.  Never hearing from them I called at 3:00 PM and asked if the truck was done and they said it was.  I went to the garage and they said that they couldn't find anything for me to come back Monday and take one of there trucks and see if it does what we are feeling.  When I got into my truck I noticed that the mileage that I dropped it off was the same as when I got it.  ( started to get smarter,  wrote mileage down when I dropped it off) when I got home I called them and asked if they had taken it for a ride and they said they seen the mechanic going with the keys and a meter.  I told them it was the same mileage when I got it as when I dropped it off.  They said when I come and take there truck for a ride they will test drive mine.  I think they just want to sell me a new truck.   any suggestions on what to do next.  This truck has been in the garage more that out.  The dealer I bought it off of said that changing transmission fluid several times takes care of the problem but GM doesn't let them do It on the 4.3L engine, what that has to do with it.   Every time we take it to the garage it comes back with another ding on it somewhere.   Really getting frustrated !!!!!!!!!!!!!!