I have a 2001 with 154000 miles lately when my suburban shifts from 1st gear to 2nd when I start out it makes a thump sound.This also happens when I get off the highway and it slows down it seems like it makes a rough shift again.Someone said this could probably be a universal joint,any ideas.The transmission seems to work fine no slipping in any gears that I can feel.Just this thump from 1st gear once I get started it is smooth.Thanks Jimbo

 

When my son's 2004 Tahoe started doing that, he had to get the transmission rebuilt. Fortunately we had had the BG transmission service performed and that comes with a warranty which paid for most of the rebuild.

 

At 154k miles I would suggest at least replacing both u-joints as a preventative, and then see if shifting improves, also consider having the slip yoke lubricated to make sure it's not the splines binding because they are dry.

 

definitely check ujoints and slip yoke but have you checked the fluid yet?

 

Check the transmission fluid level first.