Annoying Surge

First time asking a question. I have an 85 2wd with a 2.8. I am kind stumped as to whats wrong with it. It starts a little harder than it should for one. But the annoying thing is that it surges sometimes. It seems to Idle fine. but from just above idle to about 1/3 throttle it surges. Sometimes its barely noticable, but other times it seems like its rocking down the road. Doesnt do it until it warms up though. Ive replaced most of the vacume lines. Also changed plugs, wires, coil, distributer cap and rotor. And fuel pump just because I had an extra one. Any help would be great. Thanks.