Code P0174 &P0171 65 miles after LS Swap installed.

[Nodnarb76]

Hello all just finished up my LQ4 4L80 swap on my 87 Suburban.
Everything was great until this afternoon check engine light came on. Took it to Autozone and they scanned and got codes P0174 & P0171, fuel trim lean on banks 1&2.
They told me most likely a bad MAF sensor. Before I bought one decided to get people's opinion here. Here is what i am thinking: when I installed my swap, I had to mount th MAF directly to the throttle body and then mounted an new K&N air filter directly to the MAF. I've heard that it's not a good idea to mount it that close to the throttle body, would that set these codes?
Also because I mounted my new K&N filter to the MAF, Could some oil from the filter have gotten on the MAF and given me these codes? This may explain why the CEL came on after 65 miles of driving instead of when I did my first startup, just long enough to have oil come off the filter.

Opinions?