Ram tranny problems

I know this is an a body site but I was hoping to get the help of some people who know and love mopars. I just bought a 98 ram ext. cab 4x4. Everything seemed fine I got in test drove it got on it a bit and nothing. Well needless to say on my way home I hit a stop light about an hour after I left this guys place(it was a 2 hour drive) and I went to pull out and no first gear. Talk about upset. Reverse works fine but isn't the reverse and first band the same thing? It just will not pull out in first I have to baby it and if I get a hill I'm done for. What do I do? Rebuild? Junkyard tranny? If I do rebuild what's a reliable kit and where do I get it? Thanks guys and gals for all the help. Btw the fluid is full.