Vibrations, rattling and decreased gas milage HELP!

OK, I've had three seperate things all happen with the last two months. Maybe they are related, maybe not.

My 1999 Durango makes a rattling noise under heavy acceleration. It sounds like pinging except it's coming from the back of the truck somewhere.

Secondly, I am getting a bad vibration and loud thrumming noise between 2000 and 3000 rpm. The dealer said it's beacuse I got tires that are too heavy for the truck, but I know they're full of shit. The tires are Yokohama Geolander H/T-S G051. They are recommended for the Durango and are road tires. I know a bunch of other people with them eho have had no problems at all. I had them rebalanced by the dealer but that didn't seem to fix the problem.

Finally, my fuel economy has gone to hell. I usually get about 12 mpg (I have the 5.9 L with the NV242 transfer case) but now I'm getting about 10 mpg. I have not changed my driving habits and actually drive the truck less as the rattling noise and vibration are annoying on the highway.

Any help anyone can offer would be really appreciated.

Your gas mileage is the shits because you're running it at 2000-3000 rpm. With big tires no less.

Your gas mileage is the shits because you're running it at 2000-3000 rpm. With big tires no less.I'm running it with the exact same size tires that it cam with from the factory 31x10.5-15 and my driving style is the same as it has been for the last 5 years. That's why I don't understand why my fuel economy suddenly went into the toilet.

I only notice the thrumming noise and vibration when I am in the 2000 - 3000 rpm range like when I'm accelerating. Otherwise it is not present.

These are the tires I'm using http://tinyurl.com/2qepl as you can see they are highway all season. Not some crazy mudding tires.

Could be the rear u joint locked up

Could be the rear u joint locked up
Could you explain this a bit further please? Wouldn't the u-joint locking up prevent the axel from turning all together?

I remember that my with worn out u-joints, it would make some vibration and some low humming noise at certain RPM's. This does make sense. I would not say the joints are locked up else you would not be able to turn it without something snapping off. It just could be very worn out and lose, thus making your vibrating and thumping noise.

As far as your gas mileage. How many miles you have now? Have you had your injectors cleaned? Plugs and wires replaced? the usual maintenance?

Depending on your mileage, you may need your transfer case fluid changed out as well as tranny fluid if it is time.

I remember that my with worn out u-joints, it would make some vibration and some low humming noise at certain RPM's. This does make sense. I would not say the joints are locked up else you would not be able to turn it without something snapping off. It just could be very worn out and lose, thus making your vibrating and thumping noise.

As far as your gas mileage. How many miles you have now? Have you had your injectors cleaned? Plugs and wires replaced? the usual maintenance?

Depending on your mileage, you may need your transfer case fluid changed out as well as tranny fluid if it is time.My Durangobout 65,000 miles on it. I take it in to the dealer for routine maintance and they do all the specified work on it. At the last service they did some sort of engine cleaning to remove carbon from the cylinders.

I had my front suspension replaced 3 times under warranty because of the Durango's u-joint problem. However mine is a late 1999 produxtion vehicle and is not covered under the recall even though it was people with 1998s and 1999s the convinced the government to request the recall.