My 2001 yukon xl 1500 consistently flashing check engine light when cruising at high speed downhill after running for ~30 minutes. The engine preformance appears unchanged while the light is flashing. the mechanical pulled code for misfire from the computer. After driving the trk around town it resets the check engine light until the next trip. Help

That is normal for that year models, I think. Earlier cruise control just maintains the engine RPM in relation to speed. It does not use auto braking to reduce downhill speeds. Best way is to get it scanned with diagnostic scanner that can reset or check error codes for cruise control.

Without hearing it, I can only guess. Collapsed lifter or loose connecting rod bearing.

High miles? Maintenance not done on schedule? That would do it.

First I'll assume you haven't read the owners Manuel, Cruise control is not perfect on any vehicle. if coming to a hill put foot on gas to help rpm, going down hill put foot on brake to keep same speed, cruise control operates off of engine vacuum. Speed sensors can be affected by putting on smaller or bigger tires than what is on drivers door.

Its probably a problem with the cruise vacuum hose.......maybe blocked a little or the vacuum seal leaking a little. Trace the vacuum hose through to the engine area.

Check the fuel cap!! If the vacuum relief is not working it can impede the fuel flow and cause the engine to shut down or not restart after a stop. Waiting usually gives things a chance to stabalize and the engine will restsrt. When this happens again try loosening the cap and see if the engine will restart.....If it restarts immediately, REPLACE the fuel cap..Do Not leave it loose because this will cause other problems. If it is not the fuel cap the problem may be the filter, the fuel pump, or aome other fuel system malfunction.

there are a few causes for this to happen
I just put a fuel pump in yesterday in a 04 yokon XL with the same issue
it had a plugged fuel filter, and low fuel pressure.
Same complaint, coming from CA to TX, freeway speed cruise on and it just dies.

The vehilce needs to be looked at, and have vehilce scanned for codes.

I hope this helps.

Check to see if your rear blinker bulb is out.

Check to see if the power steering pump is still turning. If you have a broken drive belt (serpentine belt or "fan" belt), and the pump doesn't turn, you have no power assist. If the pump is still turning, check the fluid level in the reservoir.

FROM LUSTY KID:

Check your bulbs first, I have lost both headlights on my ford at once on account of the bulbs burning out at the same time. Same thing probably happen, you have one filament out. The lights can work, but if the filament for brake is burnt, you don't see brake lights.

As for the cruise control. Check fuse box first. If OK check vacuum hose to actuator in engine compartment for starters.
Advise:

Yup - you may need to get the grilles and such as well...