We have a !999 Bravada. Topped off the gas tank yesterday within ten minutes it started to run badly. When we were going down the highway it started to lose power. When you press down on the accelerator after you reach about 2500 to 3000 rpms it bogs down. Not being sure if we had gotten bad gas, I immediately added seafoam fuel treatment and changed the fuel filter. That did not fix the problem. After talking to others I was told that it could be blockage in the catalytic converter or possibly the mass air flow sensor. I do not smell a "rotten egg" scent. Any help or thoughts on this would be appreciated. Thanks

Grab a can of MAF sensor cleaner and give it a whirl. Your only out $5 for the cleaner. While your at it, you might want to get it scanned for any possible pending codes that haven't tripped the light yet.

Lynnlee as this is your first post...Welcome to GmForum!
You may also have some water in the tank so a few solid doses of of STP Water Remover... into the fuel might not hurt either!

Here is a link how to remove the MAF to clean it...
https://www.gmforum.com/normal-maint...cement-284332/
Hope this helps!

Is the check engine light on? If it is on, is it flashing?

i would probably change the fuel filter. and do a fuel pressure test.that happened to my Sonoma same motor about a week before my fuel pump went out.

You mentioned topping off the fuel tank. How much fuel did you put in. Considering it happened right after putting fuel in, Id check for bad fuel. Any abnormal rattle noises form the exhaust. The catylac convertors are known for separating in these rigs, causing a low power concern.

to me it sounds like either the cat or fuel pump or regulator, which is also common on those engines, you can rule out fuel though if you get a gauge(parts stores normally rent them free) and check your pressure, should be high 50'* low 60'* and when you drive it with the gauge taped to the windshield should stay there. if it drops the pump is likely bad. if you have the pressure key on engine off but it drops if you let it sit a while then the regulator is bad or you have a leak in the poppet area or tubes. of course if the pressure is fine it might be your cat

This is my first post. thank you guys for the help. I topped the tank off with 6.3 gallons of gas before the problem started. I replaced the fuel filter and there is no change. I added fuel treatment also. My plan is to get some MAF cleaner and try that today. If I replace the MAF sensor should I also replace the O2 sensors?

Also there is no "rattling" sound near the catalytic converter and yes the check engine light is on but not flashing. Thanks again for the help.

Take the car to Autozone and have them scan it for diagnostic trouble codes. They do this for free. This may help to narrow down what the problem is. Post the codes in this thread.