93 k1500 running flat in midrange

I have a 93 k1500 that I recently freshened up. I bought the truck with oil pressure problems, so I haven't driven it to know what it was like before the rebuild. Now it starts good pulls out good and if your on the highway and stomp it it takes off strong. The problem is when cruising on the highway trying to accelerate normally and just holding speed it seems very flat, enough to notice that somethings not right. It is almost like the timing is off, but it's not. i have noticed that the shift light dosen't work either, except when checking codes. has anyone else ran into anything like this. It's a 4.3 5 speed