Fj40z

Had the truck since August, picked it up with 138,000 now has 146,000. When I got the truck the PO said he had been having trouble with the tps. It would skip occasionally at light throttle, had it looked at a couple of times from a local Toyota mechanic and it will be ok for a couple of days then act up again. I changed the plugs about a month after I got it and they were covered badly in ash deposits, with the new plugs the truck ran fine for a few days then slowly started the occasional miss again. Last week it started missing a lot at any throttle position pretty bad, took it back to the shop and he adjusted the tps again and the truck seemed fine for a day. The next day I had to go on a 2 hour trip and of course about 30 minutes in it started missing bad once again. It missed all the way there but ran much better on the way back but a couple of times on the way back I could have sworn I smelled anti freeze burning so I pulled over twice and everything looked fine. Drove the truck in the shop today where i work about thirty minutes away and it ran fine outside of the slight stumble at light throttle.checked the plugs and there are the ash deposits again. The plugs must have only about 6000 miles on them. Checked the oil and it was 2 quarts low!! It has never leaked or smoked, the oil pressure was good and I was about 2000 miles from a oil change. Added oil, drove home and it ran great. The turbo seems to operate fine. I'm thinking maybe the head gasket is starting to crap out but the coolant level seems ok. I've read about the splice connections for the injectors corroding and causing the injectors to cut out but I honestly don't even know where to start. Any advice is greatly appreciated, at this point I'm ready to pull my hair out with it. Sorry for the long post.