Rick,
The 150 series is a 1/2 ton chassis. The 250 series is based on a 3/4 ton chassis. Higher load carrying rating, heavier suspension, bigger brakes, heavier duty tires, rear end, shocks, etc. All much better for towing. You give up a little in the ride comfort, but it's worth it. It's also a good idea to add a transmission cooler for towing.