Oil light flickering after complete engine rebuild

I just had the engine on my 2004 Toyota Sienna CE completely rebuilt. It is still at the mechanic's because the oil light flickered when he test drove it.

He checked the oil pressure and engine compression and he says it is mechanically perfect. After reading various blogs, I asked him about the oil pressure sending unit. He said he tested it several times and it was at the correct ohms. He said there was a communication error between the computer and the sensor. A few days ago he said he was going to reprogram the computer, but somehow it wouldn't let him (I don't understand that). I also mentioned that one of the posts on one of the blogs mentioned that changing the alternator fixed this condition for someone else. The mechanic said there have been some erratic readings from the alternator.

He is now hypothesizing that it is either the alternator or a glitch in the computer. He has a friend bringing by his 2005 Sienna this evening and is going to pop in the alternator and see if it corrects the problem. If not, he is going to check something with the other car's computer (I really don't understand how that is going to work). He hypothesizes that driving with a check engine light on for an extended time may have affected the computer (my former mechanic said the check engine light was an emission issue and it was safe to run the car. He is my "former" mechanic now). I've read that computer problems on Toyotas are rare and that the quality of the ride is typically poor, but this car has had a very smooth ride.

We are now at three weeks on a job that was originally estimated to be 4 to 5 days. He has come up with excuse after excuse and been caught in lies multiple times. He was born and raised in a different country and I read an article about doing business in his home country. Per the article, lying is an accepted social norm in his home country. My wife is very patient, but her patience was worn out a week or so ago. I've already blown up at the mechanic twice. We just want the car back and running well with the rebuilt engine. I gave the mechanic the ultimatum today that if it isn't completely fixed by tomorrow at noon I was going to have it towed to another mechanic. I would pay the new mechanic and if there was anything left over on what I owed him he would get it; if not, he was screwed. I found out that the shop he owns is not licensed in our state, doesn't have a business license, and has a non-permitted sublet of the back section of an R & D unit in an area not zoned for auto-repair, and a few other things that limit his ability to fight me on this whole issue. My preference was to pay him everything I owed him two weeks ago, but he still hasn't completed the job and I don't see an end to this fiasco unless he comes up with something tonight.

Any thoughts on this issue? I've had bad luck with mechanics lately. I have a one-man business and I prefer to patronize other small businesses. If my current (and soon to be another "former") mechanic's press clippings are correct on the internet, he was at one the Ferrari Formula One team for over four years in the late 1990s/early 2000s. He may or may not know Ferraris, but he certainly is having trouble with my 2004 Toyota Sienna.