I have a 2004 Buick Rainier and the air suspension in the rear is dropping while I am driving. If I pull over turn the truck off wait a few minutes (2-3 minutes) turn the truck on it lifts back up. What is the problem, is this an easy fix or will I run into a pricey repair.

Sounds like air suspension bag leaking. (bag instead of spring) You can convert the car over to springs again, which are much cheaper then bags, but it will not have the load leveling capabilites that it used to have. The bags cost my local repair shop $168 EACH to buy (at his discounted price from the dealer.) It literally takes about 12 minutes to change the bags on each side! It is weird to look at them when you get it off. You will find dryrot cracks which when full inflated they seem to stop leaking. But the next morning, after a cold evening, the rear end will be all the way down.

I found it destroys the rear shock if driven very far when this condition occurs. I ONLY changed my rear shock to the KYB Gas Adjust, which the auto parts store will tell you they are not applicable to your car, but if you call KYB they will give the part number too you. However, I REGRET not having changed my front struts to the same spec KYB upgraded struts to match the rear upgrade.