Okay I bought this car February 13th this year. Got it for 2500 from a boss of mine who has been the only owner since new. It has 147614 miles on it. All maintenance was done before me getting it, but that was due to a mechanic he had work on it to fix a small leak from rear main. Long story short the mechanic ended up causing alot of harm due to not installing the engine correctly after replacing the seal. Which crushed the front pump on the tranny. So then from there the person I bought the car from put a used tranny in with 80000 miles on it and had it reprogrammed of course. Shortly after changed pretty much all the gaskets water pump all the above. The issue I'm having now that I noticed prior to buying the car is a jerk as you accelerate or let of the gas occasionally. I've also loved gas mileage now down to 12 or 13 mpg city. I've went through putting new plugs in, oxygen sensor in the front, running seafoam through it. I've tried looking at the canister purge valve near the gas tank cleaned the connector out and such. I'm hitting a wall now on what it could be. Any help? The codes I have are as follow.
P1446 no dtc
P0447 evaporated emissions system vent control circuit open.
P0420 catalyst system efficiency below threshold bank 1