[snowman]

Did you replace the rings, keep the rings in the same place that they come from? Same cylinders in the same spots? Check the valve clearences?

Check the compression, the leakdown and timing (electrical) and then recheck the cam timing, just because. If these are ok, check the intakes for leaks. You can use propane to do this. If you are not familiar with this test, try just retightening all the intake nuts.

The compression test is pretty much a gold standard, go , no go. If its ok then it has to be in the electrical timing or cam timing, or fuel mixture, there isn't anything else.

The clutch, it could be the clutch, but you should have some symptoms. Starting with pedal feel. If it feels ok it most likely is. About one or two inches of free travel, max followed by a definite increase in pressure. If you got this you almost certainly have a good clutch. A double check, with the engine ideling, in first gear, let the clutch out without touching the gas pedal. Let it out suddenly, as quickly as possible, with the brake full on. The engine should die immediately, no hesitation. If it does be assured the clutch is ok.