Screwed up timing, I Think..

[camoit]

you want around 100 psi or more. Also the Jet valves can cause smoke if your truck has them.

[royster]

Also the Jet valves can cause smoke if your truck has them.

He's got the 4G64, cammoit...no jet valves.

Sounds good running, chaoticdopey. I'm going to say your valve seals are bad, by the inconsistency of the smoking. If it were rings, you wouldn't have periods of clear exhaust. Don't take my word for it, though: get a couple more opinions.

My experience with bad seals was prolonged smoking after a cold start-up, often until it was almost at running temperature. It would smoke for at least a mile before finally clearing up. The reason is: sitting overnight, oil drips into the cyclinders. The cold start-up isn't enough to burn it all off quickly, so there is a period of start-up smoking.

I also found, after replacing the seals, that it continued to smoke at cold start-up for a couple days...getting less and less each time.

I'll probably get flak from some members for saying this, but I run straight 30 weight oil in my 4G64: I found multi-viscosity allows some smoking, and this might be due to some cylinder wear, and possibly seal failure due to my not really being absolutely certain how to install them. I installed them correctly enough that mine doesn't smoke except on occassion.

Hope this is of some help to you.