99 Yukon

I am having the same issue as a few others have posted on here except with a different code.

Misfires under load. Tune up, fuel filter, and fuel pump have been done. This issue seems to happen more in warmer weather.

Misfire shows everytime and MAF sensor shows on occasion. I think it is really happening each time, but by the time I get it checked out the MAF code is gone.

Any insight to why the MAF code also is getting triggered? I should also mention that I got a Oreilly distributor cap when I did the tune up. Put it on and the car ran great for the first day. The next day it started missing like crazy. Put the old cap back on and it runs ok, but I still get the misfires under load.

The aftermarket O'Reilly distributor cap is a clue.... use AC Delco ignition parts, (distributor cap, rotor, wires and plugs). Make sure silicone dielectric is used on all terminals, inside and out, of the distributor cap. Have you checked fuel pressure and leakdown? Low fuel pressure will cause MAF codes along with P0300 series DTC's.

Is it the classic round distributor cap with the posts on top or is it the crab cap with 4 on one side and 5 on the other ( 1 for the coil )?

It has the flat cap. I replaced the fuel injectors a few weeks ago. Seemed to run alot better. Noticed I also had a coolant leak, and the engine was making a clicking noise at cold startup. Lower intake gasket was leaking, so replaced that and the lifters.

Got it out under load over the weekend and it performed great. No issues. I still have the old cap on it, but plan to get the AC delco cap soon.

Seems to be using more gas since the fuel injectors were replaced. Seems I should be getting alittle better gas mileage. Any reason why that would be?

Have you checked fuel pressure and leakdown?

Checked the fuel pressure and leakdown before putting the injectors in. It was fine. The new injectors included a new regulator so I assume the leakdown would still be good. Should I check it again?

We all know what assuming does ;)

Key on, engine off, fuel pump running, should be 60psi to 66psi and remain above 55psi for 3 to 5 minutes after the pump shuts off. Post fuel pressure and leakdown rate.