Maximum hp/torque possible on trucks?

I was just curious… Right now most light trucks (GM 2500/3500, Ford F250/F350, RAM 2500/3500) hover around having 750-900 lb-ft of torque and 400-500 hp. However, most heavy duty trucks (semi trucks, buses, fire trucks, etc) are hovering around 1,300-1,500 lb-ft of torque. Is there any limit on how much torque/hp a truck (light or heavy) can have? Limits based on frame design? Regulations? Other factors? I'm just curious because at some point no matter how powerful an engine is, there are things to heavy to tow/haul. I'm sure no light truck suspension could handle a space shuttle front tire crashing down in the bed (looking at you, Nissan). How far do you think hp/torque will go until other factors take over to say "you just can't move that"?

You are referring to the max. Engine output torque which is determined by the engine design. The lower the max. Output rpm, the higher the max. Torque. Light truck engines are quite different from heavy-duty tractors.
As for the wheel torque, it is matched to the traction needs of a particular vehicle. The matching is achieved through the combined effect of transmission and differential gear ratios and traction wheel radius.
The limits are rather high - if you can make the traction wheels move VERY slowly and avoid slipping, chances are it will pull whatever needs pulling. When the wheels can't make it, there are still tracked vehicles that may do the trick.

Some trucks are made for speed and less luggage. Some are made to be heavy. Both are different. Heavy trucks have a capability to pull huge weight in any sort of road condition. They may go only 80kmph but they can do it for any sort of weight low or high it will maintain the speed.

It depends for what use the engine is made. Caterpillar mining trucks may not go fast but carry highest weight. Road train trucks like volvo or man etc ahve higher speeds and less weights.

There's always be a limit to torque available. The industrial trucks have much bigger engines that are designed to produce tons of torque not high horsepower. Torque is the pulling power needed to move loaded trailers, pull tree stumps etc. Speed is not the big thing for those trucks.