OK so after my last post I realized my engine was no good. I picked up another used engine had a video of it running from a yard. 218k but motor looked extremely clean I would’ve never believed it had more than 40,000. I guess it came out of an ambulance van. Anyways the mechanic swap the motor in and it will not run. Cranks but no start. a manual gauge is saying there is no oil pressure it’s a 2008 lmm is there something that we may be missing? To put it in perspective we gave it fresh oil change but no oil even went into the filter even when cranking. they automatically assumed oil pump but it ran and did not run once it was put into new truck? I’ve never heard of an oil pump just crapping out like that. Is there some special way this is supposed to start after a swap? It took the mechanic almost 6 weeks to put the motor in so it’s past the 30 day warranty due to them being slow. I’m basically being told if it’s an oil pump I’m gonna have to pay for it. So pretty much I’m just trying to figure out if there’s any other possibilities. Any replies are greatly appreciated.