I left work today and was pulling onto the highway, when I noticed I had my foot about 3/4 on the gas (as usual, because of all the traffic coming) and it felt like it was bogging down because my rpm's weren't even reaching 3000 (and they're usually around 4000 at this point), then I hit 25 mph, the truck shifted gears (auto tranny btw), and it drove fine. Continuing on my drive home, I noticed every time I accelerated from a complete stop I had to put my foot down. The truck would then shake (pretty bad) and the rpm's would struggle to get to 2500 up until I hit 25, and everything was fine again.

I'm pretty sure the vibration was coming from the rear end. Not sure if it's a fuel/timing problem, or if my rear end is about to go...any thoughts will be helpful.

 

any check engine lights? maybe check some of your vacuum hoses?

 

Did some research, pretty sure it's a bad catalytic converter.

 

Had the same issue with my Blazer, ended up being a clogged fuel filter and the points in the distributor were almost gone. I had assumed it was the cat in my situation too.