P0300 and P0102 codes after engine replacement

[cory30189]

I have a 03 blazer with 154k miles on it and just put a used engine in the vehicle with 56k miles on it. After we completed the job i went for a drive on the interstate and at 70mph the check engine starts flashing and sets P0300 random misfire code then goes away. I removed the distributor cap and found moustire inside so i replaced the whole distributor and cap and rotor. Went back for another drive and is doing the same thing. Everything is new on the engine basically, replaced injector syster, new plugs, new wires, new cap and rotor, new fuel pump. our master technication is helping me but we have no access to GM info and when i called a local dealer to ask if theres any procedure after i replaced the engine and he had no idea what i was talking about. I read a couple things online about having to reflash the computer and do i crankshaft position sensor relearn but i cant get anyone to confirm this. Also this morning coming to work i set a P0102 code for MAF circuit input too low, im not sure if all these connected together but im completly stuck and tried to get some help from the dealer and they keep blowing me off.