1999 Nissan Pathfinder Ongoing issue with bucking

I have a 1999 Pathfinder SE with 288,000 on the truck, and approximately 145 thousand on the second engine. The issue is when the truck is cold it runs fine, but when it warms up it starts to buck. We pulled the check engine codes, and it said the M.A.P sensor so I changed that, and cleared the code. I also changed the wires, cap, rotor, and plugs, and air filter the same day. Everything is tight, and functioning but than about a week later it started again. Runs fine cold than once at operating temp it starts to buck between 2000-4000 rpms. Only this time once it was warm it also started to stall at idle, and the light came back on. It said the knock sensor, but since that doesn't throw a code, my mechanic and I deduced (using his alldata program) that it could be the camshaft positioning sensor so I changed that as well. Still no luck. I cleared the codes again, and haven't driven it enough to run an ecm cycle...any ideas where I can go next? It doesn't seem to be a clogged cat although it does seem to run lean, and is missing at various intervals. Suggestions? We wish not to put a ton more money into the thing as we know it's not going to last much longer.

Sept 16 edit: I have cleaned the EGR valve, and tested it, tested the catalytic converters, checked for vacuum leaks. None of the above apply and there is still no check engine light.