High rpm low acceleration after I hit 2500rpm

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I have a 1998 Dodge Ram 1500 318 5.2 sport....I have experienced a issue where when I am driving either up a hill or I accelerate hard. When I hit 2500 rpm and stop to go again or slow down. The rpm will rise and won't shift and my speed goes up slowly. I have had my transmission looked at and is in good shape. I am not sure what is going on here. I also am running a Straight pipe no muffler with cats...PLEASE HELP