There's a lot of talk here about engine power, which is the least of worries when towing an overload and haven't seen an engine yet that couldn't handle most. That is unless it can't get the required air and overheats. Most problems begin with the tranny when pulling long steep grades and the downhill that comes afterward. Toad brakes are now really required as using the lowest gear possible if the rig isn't equipped with an exhaust brake or other. In other words, overheating of something is usually the problem with climbing and smoking the brakes and boiling the brake fluid if not air equipped when going down.