First long trip... got problems. Not happy.

[OrangeCrush]

Okay, got back to NC from Fla. late last night. This is my first trip with the lift kit. I wasn't sure after installing the 4.56 gears if they would make up for the 38" taller tires.

First, I am truly disappointed in the performance. I installed the Volant air intake, 4.56 gears, Magnaflow exhaust and the SuperChip's programmer. I wasn't expecting seat of your pants performance difference but was hoping for something...anything.

The entire 1200 mile trip, I averaged 10.0 mpg. I was running 80-85 down there for the most part and stayed under 80 mph all the way back.
I realize that the gas mileage drops at speeds over 55 but I thought I'd at least average 12'ish mpg.

Secondly, I didn't notice on the way down but on the way up, I COULDN'T drive over 80mph. I'd get a terrible vibration. I don't think it was anything to do with tire balancing as a)usually you can feel it in the steering wheel fairly easily. and b)if you do have a tire out of balance, it's not normally in the 80mph range and if you increase the speed by 5-10mph, the wobble goes away.

My vibration felt in the drivetrain and stayed with me until I hit 95mph. I don't know if it would have gone away at a higher speed but bad tire balancing usually goes away 5-10mph faster.

Has anyone using the Fabtech kit had a vibration problem from their front driveshaft? I've had enough lifted vehicles and to me it feels like the front driveshaft is out of balance. Anyone else?

My third complaint (and this might have been me) is you can't leave the cruise control on at 80mph. It will go into passing gear in a heartbeat. I know the 4L60e transmission shifts by mph so this might be my fault. Before I left town, I used the Superchips programmer to move the shift points. I extended them by a couple of clicks so it would stay in gear longer before it shifted. Would that have affected how easily the trans would go into passing gear. It's like the kickdown setting was low. It wouldn't just drop one gear, it was going down two gears when the cruise was on.

Of course, the truck is so gutless, going up any kind of incline, it would at least drop one gear if I wasn't using the cruise.

I'm going to look into a supercharger. I can't drive a vehicle on the highway that can hardly maintain an 80 mph speed...

Any help or suggestions would be appreciated.

Mark