Codes P0171 and P0172

It started off with getting little hesitation when driving up hill. Was told that injectors was bad. After replacing the injectors and start, the problem was way worst. Took it to a local mechanic scanned it had error codes on my personal scanner p0171 and p0172. Mechanic had me replaced intake manifold, temperature sensor, canister purge solenoid, neutral backup switch, crankshaft position sensor. Still did not solve problem. I had the fuel pump spark plug replaced previous. However still did not solve problem. When vehicle starts it would just misfire/back fire and hesitate and stall. I told mechanic to put the old injectors back in for me to move the vehicle when that happen it started and worked way better than it was before. So before I took vehicle home he said he will clean injectors when he did it still hesitant on flat and worst up hill. Fuel filters also was changed. The mechanic had the vehicle run on e I had to buy gas and fill for it to start so I am not sure if somehow the dirt from bottom blocked back injectors as such. A fuel pressure test was done previously and it was fine according to mechanic. Please advice on what am I missing. I plan on fixing problem myself.