Will not crank Spark plugs were replaced?

Last October the fuel pump went out. I bought one from eBay and a friend of mine who's a certified mechanic put it on. Immediately the fuel efficiency was worse, and it would barely accelerate up a hill. Then a couple months later the check engine light came on. I can't remember the exact codes but nothing major. Spark plugs were replaced and something else I can't remember. A couple weeks ago it wouldn't shift into fourth gear. Mechanic friend of whom I don't think I can trust anymore and shouldn't have ever trusted said that it was in limp mode. It seems to come out of limp mode after it's drove for a little while and drives fine except for the same acceleration issue. I was told to get a MAF sensor but then told that it wasn't the issue even though I was under the impression that it was the code thrown. Now it acts as if it's out of gas but it's not. Fuel pump issues again apparently.