An F-150 with Max Tow can handle anything that any half ton is capable of and will come fully equipped with coolers, the correct gears, etc.

Do you know what your axle ratios are? The 4.6L 3V trucks were built when there was no V-6 offering and it was intended to be the most fuel efficient of the line up.

Have you given any consideration to purchasing and extended warranty? The Ford ESP may not be an option because you're beyond the 3/36K mark. Your dealer maybe able to assist you with another option.

I don't know much about tuners but if you plan to keep the truck for a bit, then it maybe cheaper than paying for a reflash every 15K miles.

Additionally, since you tow frequently, you may have the dealer do a transmission fluid exchange and see if that makes any difference. Supposedly the Mercon LV fluid is good for 150K however, you may consult your owners manual and see what it says for your model year truck for severe duty use.

My last suggestion would be to trade the truck and start over. Keep us posted sir and welcome to FTE!