1999 dodge ram 1500 sport limp mode?

I just went out and bought my very first ram truck (after owning ford my whole life) it's a 1999 1500 with the 5.9 gasser in it and I abosolitly love this truck! Well at lest I did tell it went limp… I was driving to the lake with a few buddy's on the freeway and I was just crusing at about 75 when al of the sudden my truck high reved and wouldn't go faster then 35-40 I've done some asking and some research it seems like it's the govner presser switch and cylonoid but That's just what I read online. I don't just wanna through parts at it and wast money so any ideas?
Little more In to it.
Around town driving it dose awsome but I'm only geting about 6 mpg and it won't shift out of 2nd gear it just reves about 2500 rpms and wines. I can't go faster then about 45 down hill and it will shift from 2nd to 3rd if I let of the gas but as soon as I go to give it some throttle it will down shift. Could really use some help here

Chances are that you have a serious transmission problem. It is in "limp" mode, so you only have 2nd and reverse. You can't keep driving it like that. See if a complete fluid flush, and both filter changes help. Otherwise, it's overhaul time. Make sure they use the right fluid. I believe it's ATF+4

Is there a check engine light on? Being in limp mode you might have a problem with either the governor solenoid or sensor. But one or the other should set the light off. Find local shop at ATRA.COM for more help