B4000 loses power check engine light on
 

I just picked up a 94 B4000 pickup with a 5 speed. The truck idles great and will rev up fine. Here's the problem if you bring the rpms upslowly when it gets to 3500 it feels like the fuel cuts out and the rpms will drop back down to about 1100 and then it will be allright again until it gets up to 3500 rpms again. The truck doesn't completely die out.The check engine light is on steady until the truck acts up then it goes off when it loses power and returns when the power comes back. When I drive it I can only get about 20 feet before it's starts bucking and trying to stall unless I ride the clutch to get it going but as soon as it's under a load it acts up.I would like to get the codes out of it but I need a hint on what to do and where to get them from. It's a decent truck and would like to know what to change instead of guessing.Any help would be appreciated.