Here's the issue, the truck seriously loses power going up into the mountains. I have already gotten the fuel injectors cleaned and a full tune-up. I know it isn't the clutch, since I know from experience what that is like, and it doesn't have an altitude adjustment thingy (I don't know the technical term).
The truck is getting a bit old (approaching 150,000 miles), but in all other aspects it is still a great truck. It's a '93 Toyota SR5 V6 pick-up. I really don't want to have to replace it yet, since it really is great other than losing power, but I am worried it won't be able to pull the tear well.

Do any of you have ideas about what might be happening? I am totally at a loss here,
Amy