Everything is Calgary is expensive. We are also the second most expensive place for parking in North America right behind New York city. A monthly parking spot downtown goes for $500.00 to $600.00 or more a month.

 

Truck weight spec in your 03 manuel page 167 shows 5216 lbs..
The GCWR is 11,500 lbs. for 16 inch tires.
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Truck weight for 17 inch tires is specd at 4990 with a GCWR of 11,000 lbs.
Don't know what your stock build came with but larger diameter tires changes the final drive ratio in the wrong direction for towing.
Also little known is that common P tires (non LT rated tires) are derated 10% on load rating, for towing.
Bottom line is when towing near max gross there are a lot of additional factors that can come into play.
Most either ignor them or try getting away with it.
Some examples are axle weight rating, tire load rating, less then the best brake lineing and performance, engine cooling plus a number of items determined by the state you live in.
Most of the time pulling at or over max shortens life of many parts.
For example pulling steep hills on a regular basis puts huge stress on the torque converter if your in low gear at wide open throttle.
The fluid is tying to force both halves apart, called ballooning.
There are flat roller bearings on the pump side that has to take those loads from ballooning.
This is where lower gear ratios are helpful so not so much torque has to be applied by throttle.
For example if the torque required at any given moment were 100 lb/ft to move the total load, the gear ratio being used at that time multiplies the engine torque to that value.
If the gear ratio were lowered the engine has to supply less torque because it was multiplied by the lower gearing to attain the same value.
But you don't get away free with this because the engine RPM goes up, it may make more torque from higher RPM so somewhat less throttle opening may be required to maintain the same road speed.
This would be less stress on the torque converter from the engine..
Just info you need to know about.

 

My 2000 SCAB 4x4 weighed 5200 lbs with me (250lbs) and a Leer shell on the back at the trash dump. They weighed it before and after to know what to charge.

I once towed a 25' travel trailer from Raleigh NC to Orlando with a 1986 SWB F150 with a 5.0L engine and C6 3 speed auto with a 3.08 rear. It did fine. At 65mph on I95, the engine turned about 2600rpm which was right at the torque peak.
Bottom line is you can tow anything with anything if you take your time and have enough cooling. I didn't even have the additional trans cooler on the 86. After I got back, I bought the factory cooler from a salvage yard and bolted in on. there were predrilled holes in the truck for bolting it on. I also bought the Reese dual cam sway control and installed them on the Reese weight distributing hitch (1,000lbs bars). It swayed on the trip especially when a truck went by.

 

An important point to make is the 4.6 peak torque is at just over 3200 rpm.
If you tow fast enough to make that range fine but most don't want to pull any longer than is needed like that unless it's a hill and the need is there.
At this point you would switch OD off so the converter will lock up otherwise the trans will run much higher temps in an unlocked condition.
Pulling under 2200 rpm and there is not much torque being produced.
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The 5L motors usually had peak torque in the 2200 to 2600 range but was done pulling hard at about 3800 to 4000 rpm.
The cam timing is shorter than in a car application and the intake has long tuned runners to enhance the torque range.
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My 4.6 begins to pull harder at about 2100 and continues to get with the show past 3200.
With a 4.6 don't be afraid to wind it a bit to get the job done.
Lugging is not any better that winding higher RPM.
These are important parameters to understand when going to a tow application as long as it's not overdone with to heavy a total load.
Good luck.