First of all, why aren't you using 3rd gear? It should maintain speed up those grades a lot better in 3rd. Yes, it will be revving high, but that's where the power band is. With my old rig loaded (86 4runner), I could usually stay pretty close to the speed limit over Donner summit as long as I used 3rd.

A Tacoma would suit your needs too. More power and torque. The autos are good in those newer trucks. DOHC engines like to rev high though. Some of the Taco's have manual hubs, and most or all can be converted.

And CA laws leave plenty of engine swap possibilities. All it has to be is the same year or newer and you have to keep all the smog equipment installed. That said, I don't think any engine swap is really worth it unless you are really attached to your current truck.