ok the only modifications to the truck is Torsion bars and exhaust...

Exaust gutted cats broken rear 02 sensors single 14in glasspack..miss the no muffler but the highway patrolman that lives in town doesnt HA

-=-04 QC 4.7L Manual 5 Speed-=-

well even with the downstream 02s broken i got between 16-18.5 sometimes 19 20 MPG highway for 2500 or so miles then i put the glasspack on 3 days later..boom sudden drop from those MPGs to at 65 in OD i get maybe 9.5 if im lucky and i pull a trailer with a car behind me STILL the same gas mileage but when i leave from a stop sign and get on it "first gear" it will hit 3500 RPMs and then suddenly act like a carbeurated truck flooding out which also triggers my p0300 code"multiple missfire" and blows black smoke till about 4000-4250 rpm then suddenly take off like it took in a shot of nitrous. if anyone has any ideas please post. and u dont have to say get new 02s ive got them on order should be in sometime this week. but since it didnt do this till i put more backpressure on the exhaust i dont think its them tho i could be wrong

 

Seems like you better get those O2 sensors replaced. They are what adjust the A/F ratio. I'm surprised you don't have the check engine light and codes, cats gutted or not.
I would imagine that if you leave it like it is now, you'll end up with a heavily carboned engine.
Almost sounds like the engine has set itself in the "limp" mode. You might want to check and see if the PCM has thrown any coses

 

oh yah sorry forgot i got both bank 1 and 2 sensor 2 on each codes along with the P0300 multiple missfire but its only on the right "passenger side" of the engine because i just pulled the old 02s and only the right one was filled with black soot "carbon" so it must have only went limp on the pass side the drivers side was clean as a wissle the peice in the middle that i broke "porcelain" was still white on driver side but black and covered with about 1/8 of carbon the drivers so when i get the new 02s hopefully the problem is fixed with the new 02s when i get them. i have one coming in tomorrow.dont know about the other so i beleive i will be throwing that one on the pass side and reset the PCM..."battery connection disconnect" then hopefully when i do the key on key off i only get the Bank one sensor 2 and not bank one and two since it looks like the P0300code multiple misfire is probaly coming from the pass side sensors and will hopefully lean it out a bit and stop with the soot throwing god damn thing looks like a diesel when u get on it lol but ya time to get back to fixing other things ttyl any responses will be helpful

 

You are going to have to replace the O2 sensors, simple as that. It kinda sucks, but that is what you are going to need. Luckily they aren't super expensive and easy to find at your local aut parts store

 

got one 02 sensor in waiting on other at first they orderedme 'Standards' but the catalog was wrong and they dont have anything in the intown store but they ordered me brand new NGK ones that are 114 dollars a peice but since he priced me the standards at 32 a peice hes giving me the NGKs at that price. with one replaced i found out only my pass side was rich now it runs fine and back to getting 15-19 mpg highway about 22-27 at 30 with the cruise set dont bother me haha