rkennedy1,
You have basically the same drivetrain I had in my '01. 5. It wouldn't pull a slight grade in OD, empty. My new truck rocks and can haul a load uphill in OD that the SO couldn't do empty. The OD ratio in the autos (47RE's anyway) is more of a jump than on the manual's. Makes the problem even worse. I learned my lesson this time and bought what I should have the first time, a HO, six speed. In all fairness, I didn't get to try a HO with the 48RE, but I knew I wanted the NV-5600 no matter what.
If you can get DC or the Dealer to do anything for you, I suggest getting the HO, if not and its really bothering you, then you may want to just add some goodies for more power. Downside: probably kissing your warranty goodbye.
good luck
Dave