2001 dodge ram 1500 5.2 liter 87k miles

The problem as described sounds like your catalytic converter is clogging/clogged up, when it comes to the power problem. Remove the front O2 sensor n let the engine run. Yes, it'll be loud, but if it starts easier and/or gets some power back (use the vroom, vroom method to see if the engine jumps rapidly in RPM). It'll also set off the check engine lite, but don't worry about that for now. You could also go by a reputable exhaust shop or mechanic; they can usually tell pretty qwik if the cat is clogged. Shifting at 3K could be either the tranny goin bad (valve body or solenoids). When was the last time you changed the tranny fluid? Good luck!