99 Yukon misfire!

[operator556]

My 99 Yukon started having a misfire about a month back and I went through all the usual things until I cleaned the injectors and it sort of smoothed out. Until I was pulling my jet ski and it started doing it again. Only misses in between 2-3k rpm while under load (hills, trailering, above 1/2 throttle) now I've been watching the coolant and its eaten about a half gallon in the past month but there is no sign of it in the oil....intake gaskets? Codes are P0300 and P0303

[1997SierraSLT]

coolant loss is most likely internal. there are numerous threads on the poorly designed intake manifold/gaskets addressing this issue. I replaced intake manifold gaskets three times before finally dumping it at 167,000 miles on the odometer.

 

Chased the P0300 for 16 years to no avail. replaced CSFI with upgraded MFI system, new fuel pump, new fuel filter, new spark plugs/wires, new MAP sensor, new O2 sensors.

[operator556]

I'm debating on just throwing the carbed 383 I have sitting in my garage in it and calling it a day. I'm so fed up with this misfire nonsense

Truck doesn't leak a drop of anything so it has to be eating it