Engine loses power when excelorating
on 1999 GMC Yukon

Engine starts and idles fine, but stumbles when I press on gas, and won't cruise past 100 kph

Asked by for the 1999 GMC Yukon
review when last tuned. it may just be due.
try oil stabilize in engine to recondition seals and cylinders. this will enhance compression.
use ethanol treatment on next fill up. this will clean any ethanol resins that may be inhibiting fuel delivery.
do fuel pressure test to check.
run diagnostic to find any other issues you should be aware of.
consider upgrading air filter to high air flow design.
1 more answer
i had the same problem. it was the ignition control module