High idle solenoid

[funnyman06]

So im not sure if this is normal but when my high idle solenoid is on the truck is like 10x more fun to drive. It seems to have more oomph and will put you back in your seat (all things relative) but when it turns off the truck is a dog compared to where it was. Also when the solenoid is on the truck doesn't smoke no matter how much throttle you give it, it just takes it and runs.
Is this a result of incorrect timing? I seem to get great gas mileage but the truck is a dog compared to when its on?

 

[Agnem]

The timing advance is active when your solenoid is on, so it is the timing advance that is responsible for your new found "umph". In all likelyhood, your timing is in need of adjustment. All pumps retard with wear, and should be checked every 10K or so.