since you already had the ideal pulling truck, you know the obvious answer..
but if you're looking for cheap, light, and comfort, 1/2t will handle that 4500lb rig all day no problem..
to make your tow as safe as possible, I recommend brakes on both trailer axles.. they usually only have them on the rear, have a local trailer outfit install one on the front.. weaker brakes is the biggest downfall I see with lighter trucks towing.. although at 4500lbs you'll be well withing safe limits on a 1/2t, extra braking over mountains and steep grades is a nice safety factor, especially for only a $2-300 axle..
I also recommend a good controller, if the truck you buy doesn't already have an OEM installed, prodigy is one of the best out there..
this is an old '02 GMC 1500 with 5.3, towed ~7500lbs frequently from baja to mojave no problem other than predictable trans which made it to around 120k miles and still drove to trans garage..
mine being early, also had the weak heads that both cracked and started drinking a gallon of coolant a week.. cheaper for me to replace the engine than both heads on 150k mile engine so swapped it.. but even with both heads pouring coolant out, drove it to father in laws shop in henderson 90 mph in 115 degree heat only stopping for gas once and water three times
at 190k miles, still drive it daily.. paid off in '04 and that was the last car payment I'll ever have
bottom line is they have plenty of power and longevity with sensible driving, normal person probably could easily double my results
good luck!
