Ive got a 77 ford and i need help picking a cam. I want a nice lope and good power at all rpm's but I would prefer to have it down low. The truck is an F250 on 39.5's, it will be used offroad.

 

Look for a cam with more duration on the exhaust side then the intake. A good choice of cams is something in the comp xtreme 4x4 series of cams (or if you want some other company use those cams as a guide for lift and duration figures.)
Remember lope does NOT mean more power it means the cam is more of a high rpm cam and will lose low end. But you can get a slight lope without losing too much low end but it's a real delicate balance there.
As to which cam, well you haven't told us about any other modifications like headers? what intake? etc.

 

going with an edelbrock intake, ive got DOVE heads, a predator carb, thinking about a set of L&L headers, but right now ive just got stock manifolds. But, thats going to change real soon. Thanks

 

get some kind of headers on it. the exhuast is the major restriction on these engines.
If your going with the performer intake you want the lowest of those 4x4 cams comp offers since it's not much better then a stock intake. If you go with a performer rpm or a weiand stealth then you can jump up to the x262H-11 which willl have a little bit 0f an idle but still be a good all around cam.
Also I would get rid of the predator, yes they work but they are really not a street carb at all. fuel economy stinks and the only time they actually work correctly is WOT. I ran them for years but found that a properly tuned Carter AFB (edelbrock) or a Holley will outperform them. Major strong point of the predetor is it's an odd ball and people notice it so a great conversation piece

 

i always ran a dual pattern cam in my small blocks (more exhaust dur.) but i recently went to a 218-218 speed pro cam in my 460 and it works great! tons of low end torque, can use the stock springs (.495 lift) and it even has a little lope to the idle which i was surprised about. i wouldnt go bigger without a stall in an auto trans though. cheap and a seemingly great mild peformance cam in a near stock engine.