Tires: Truck tire pressures vs. load, 5th wheel hitch, truck axles

Question
QUESTION: I have just purchased a 2009 GMC 2500HD 4wd truck. The tire pressures called for on the sticker are 55psi front, 80 psi rear.
I drive the truck in one of two configurations only; towing the 5th wheel in which case the pin load is 2200 lb and I will use the specified pressures.
The other configuration is with two passengers only. We use my wife's Honda as much as possible, and I do not take the 5th wheel hitch out. In that configuration the ride is very harsh.
I have just weighed the truck axles on a public weigh scales with no trailer, two passengers, full gas tank and get 3760 front, 3092 rear. (1880 lb ea. front, 1546 ea. rear)
I am unable to find pressure/load charts for the Bridgestone LT245/75R16 Rib 265 tires. Please advise what pressures I can come down to for those axle weights.
I understand that if I ever put any other load in the truck I will have to go up to the spec pressures.
Thanks, John

ANSWER: John,

Can you tell me what the placard says about GAWR's?  That information answers the question of what reserve tire capacity GM built in to the truck.

---------- FOLLOW-UP ----------

QUESTION: Barry,

From the placard:  
9200 lb total , 4200 lb front,  6084 rear

John

Answer
John,

Thanks for the info.

An LT245/75R16 has a load carrying capacity of 2335# @ 55 psi, and 3042# @ 80 psi.

GM lists the GAWR's as 4200# front / 6084 # rear.  That means there is a reserve capacity of 4670 - 4200 = 470# front / 6084 - 6084 = 0 rear.  (side comment:  I don't think it is good engineering practice to use 100% of a tire's load capacity at any pressure, especially the max!)

So if you've weighed the truck at 3760# / 3092 # - then if I add back in the reserve load I get 4230 # / 3092# - which means the MINIMUM inflation pressure is 48 psi / ....uh .... Well, the chart doesn't go below 35 psi - which I think is the absolute minimum pressure for an LT metric.

But I think preserving the ratio front to rear is important to maintain the handling - so I'd recommend using 50 / 75.  

OK, that doesn't quite fit the way I'd like it to.

If I add the resve capacity of the front onto the rear - 3092 + 470 = 3562 - which mean a minimum inflation pressure of 38 psi.

OK, so as a compromise, I'd recommend using 50 psi all around in the condition you weighed the truck in.