I had that exact truck for a few years, got it new. What I remember most about it was that the MPG's really sucked. 12-13 mpg as I recall. I hope you got either the 35 gallon tank or the dual tanks..
...and yes, that's a smog pump, and if you disconnect any hoses from the engine, the should be plugged. You might want to check your mileage with and without that pump hooked up, though.