Dodge B2500 Looses Power Uphill

I have a 1996 Dodge B2500 with 5.9L V8. About 3 months ago, the AC would cut out when I would be accelerating up hills, usually steep hills or at high speeds. Cool air would come out of the defroster and floor vents when it happened. Happened a lot, but it would come right back when I eased up on gas pedal, so didn't worry too much. Then I noticed the heat do the same thing twice in the last week. It would cut out alltogether. On a long trip for Thanksgiving, about 5 hours into a drive, of running flawlessley, heat working well, I was going up a mountian on the highway, and the van started shaking violently and loosing power, I let up off the gas and it came back, ran OK for a while, just couldn't accelerate too quickly. Within 15 minutes, I couldn't accelerate at all, had to get towed to town. When tow truck lifted back end, brake lights came on, and the van lost power brakes. Getting codes for misfire on cylinders 1,2 &3. Plugs, wires, cap & rotor look OK, as well as air filter. After sitting for a while, fuel pressure was at 40, but problem is at higher load, not just sitting. Now the old Dodge runs at idle and low speeds, still no power brakes, haven't tried higher speeds or hills lately.

Answered you on another forum.