Coming from an 08LMM Duramax, this is quite a different experience. 02 2500 CCLB with a loaded bed and 7k? Trailer.
Just wanted to document my observations.

Towing through Oregon And currently Idaho on the interstate, im spending most of my time in 2nd gear over 4500rpm , over 50%tps and AFR in the 12's. The motor and trans are working hard and the trans is running warm, dash Guage stays over 200-250 but I should check with VCM to see what it's actually at.
idaho sucks because speed limit is 80 and the constant hills. Towing at 70 is way more comfortable than 80, the lower mph and tps% means more time in 3rd gear. Kind of ironic that more speed means lower gear .

I know I need a better trans cooler, and everything would be happier if the motor made more torque. Trans is constantly kicking down into 2nd.
fuel mileage is anywhere between 5.5-6.5. Garbage.

I have a transmission tune and the TCC stays locked most of the time. Running in D3 keeps the TCC engaged for engine braking on downhill grades but honestly I haven't needed it near as much as I thought. On flatter ground I sometimes run in Drive to see if I can get it to shift into 4th but this virtually doesn't happen. Owners manual says it's fine to tow in drive, which I never knew.

My takeaway is that this truck will do the job but for towing I miss the diesel and 6spd Allison. I think a turbo and bigger trans cooler would be significant improvements .

 

You cant beat a diesel for towing.
Diesel that makes 800ftlb torque at 2000 rpms and your making about 250ftlb torque at the same rpm. Makes quite a difference towing.
What kinda trailer? Enclosed?

 

Boost all the things

 

this trailer weighed 7k at one point but is pretty loaded down at the moment.
4.9mpg last fillup.... ffs. Tremonton UT.
I knew gasmotors would run in the 12's at WOT but I've never seen AFR's in the 10's. I just installed this wideband setup so im still learning, previous experience was with motorcycles on the dyno.

 

Gears.

 

She looks pretty loaded. Are those aftermarket wheels/tires? That will affect your overall drive ratio.

What gears do you have?

I think a larger transmission external cooler would definitely help. I think the factory ones were kinda on the small side.

If the truck can't achieve 4th gear, probably best to leave the transmission in manual 3, even though Owner's Manual says you can tow in D.

 

Yea i wouldnt want to haul that thru the mountians haha.
They will run in the 12s if the MAF table is tune correctly.
Datalog it with MAF Frequenzy and wideband input While in PE and if your seeing 10.6AFR at 8000Hz then remove about 15% from that cell and smooth the table.

 

That wind sail of a trailer must really slow you down. I've pulled 5k to 10k trailers with vehicles or flat stuff through the Idaho mountains fine. I even calculated about 9 to 10 mpg with those loads, but speeds were lower too, mostly 55 - 65 mph.

After putting the Tru cool 40k on my truck, trans temps have always been good.

 

COT aka cat over temp will easily send the air fuel ratio into the 10's to cool the cats back down. If that is still enabled, that is why the AFR drops.

Most heavy duty trucks run an EQ ratio around 1.200-1.250 which is about 11.7-12.25 commanded AFR in PE.

 

She needs the RPM to make the torque. The only way around that is boost, and even then you will want 12-12.5 AFR at the most

It's not very efficient to tow with a gas motor, but she will do it better with some mods