2001 Hyundai Accent 4500 RPM's at 60. Dosent seem to be shi

First of all it dosent do this all the time. I'll know if my car is going to act up by the time I get to the first stop I come to, sometimes when I shift from P to D or R to D the tranny will shutter or it will shift fine but do it when I just start to take off or come to a stop. After it does this the car dosent shift as it should, it feels slugish like its fighting to drive. And when I get it on the highway it dosent seem to shift at all, under normal cond. At 60 the RPMs will be at 2500 when its acting up there at 4500 and the engine sounds like its working way to hard. I had it put on the scope and the codes it was sending said it was a vacum pressure prob. And that the D shift cylinode was bad is this it. If so what is the ball park cost for such a repair. ANY FEED BSCK IS HELFUL AND MUCH APPRECIATED. Thank you