Oil sending unit

Alright I got a question about my oil sending unit. I bought this truck about 3 ago and it has not been taken of. I drove it five hours motor ran great. Guages read like normal l. No problem. Got it home changed the oil. There sludge all in the oil filter. Ended up having to buy a new oil bracket and I took my oil sending unit off. When I got the new oil bracket I connected my oil sending unit. But now I'm reading low pressure. Could it be i don't have the sending unit screwed in far enough. How do you test the sending unit?

 

Shoot us some additional info like, which year and motor option you have. Will help.

 

My bad I thought I did. 2016 toyota tundra sr5 4.6L

 

Since there was sludge in the oil filter there is probably more in other parts of the engine. What did the under side of the oil cap look like when you changed the oil? You could have more sludge in the oil pan, it could be worth your while to remove the pan to inspect. There are some sludge removing products that you add to engine oil, run for a short period of time and do an oil change. I have heard of some people using a diesel with oil and in a few rare cases running 100% diesel for a very short time than an oil change. There are some YouTube videos on the subject