When my blazer is going down the road a highway speeds, 50 - 65 mph, I will get a change in the rpms of about 3 or 4 hundred and the you can feel the truck hesitate. It kind of feels like the transmission is slipping, but it only does it at highway speeds, any ideas?

 

First thing check your fluid level and condition. My wife had this problem a couple weeks ago, it was just low on fluid. It could also happen if your fluid is just old. If you are low on fluid or decide it need a change add a bottle of TransX. I don't usually use additives but this is one I've had multiple mechanics tell me to use, it fixed the slip between 1st and 2nd on my rig. If that's not it you probably have a band or two in you trans getting toasty.