When I first start it is normal, very little black smoke if any, after 30 minutes of driving or so (city). I feel like there is NO power and there is tons of black smoke. It starts clearing as it climbs rpm's and as soon as it shifts it is right back to the "bogged" state.

It is a '98 k2500 it has a 3" dp with a 4" exhaust. That is it. Also no gauges at the moment. That is next. It has 75,000 miles on it.

Any advice on how to clear it up. Also, it didn't occur last winter. On colder days it isn't near as bad and when the AC is on forget about moving after 30 minutes.