my guess will be converters. wild shot guess without enough info lol.

 

I don't have any lights on or any codes showing. Maybe the dealer can fix it on Monday.

 

Update if they find out or if ya find out first, Also how many miles on your converters are they oem or after market. If you used after market converters did you get crappy ones, thats the only way i can think the converters have gone since the truck is an 08 unless he is dumping GOBs of fuel at it and has melted them but thats a long shot.

 

It's a 4.8 right..

 

Yeah it's a 4.8 and the Cats are OEM to the best of my knowledge.

I'm starting to wonder if might have had a tuner or something on it before???

What's throwing me off is my Speedo. I was driving next to my mom the other day and she said I was going about 10mph faster than what my Speedo was registering. Not to mention, it shuts off at 80.

What would be the cause of that? The rearend doesn't look like it's been messed with so I doubt it has a different set of gears or anything.

 

what size wheels and tires are you running?

 

Got a hand-held GPS? Could be your Mom's speedo is off that much and yours is fine ....

 

Maybe it had a programmer or some kind of tune... I know mine was fully stock... I would get 11-12 mpg
On the street.. But that's mainly doing city driving... This truck ain't that great on gas.. Truck for sure had some bigger rims and they probably program it for those bigger rims...

 

Stock 245/70/17

This is probably true, I didn't think about that.
So could the dealership fix this or should I start saving and go get a custom tune?

 

I say .. I rather get a real tune... U will see some better mpg... Plus he can tune it the way u want it... For towing... Regular driving etc... And fix ur speedo...