Runs and drives but starts to skip at about 30 mph

You don't give me much information to work with. However, 1st, look at the engine mounts. You may have a broken mount. This will make it feel like the transmission is shifting hard. Other than that, there is only a few things that will cause this. The speed sensor tells the computer when to shift the shift solenoids. It may not be "seeing" a quality signal. If this is the case, the speedometer will be bouncing too. Last idea is that it is skipping a gear. Starts in 1st, should go to 2nd at about 10 MPH. 3rd at 25 to 30 MPH. And, if you have a Overdrive transmission, it should go into overdrive at around 45 to 55 MPH. If it is skipping 2nd, it will engage 3rd at a high engine speed, and will feel like a sudden slam into gear. If this is true, your transmission needs some work. Hope this all helps. Good Luck.

check the alternator... battery isn't getting sufficient power from it. if tthe problem continues there will be chance of battery dead. duo to the less power supply from alternator, if we increase the rpm though the vehicle wont go faster and engine gets off. so my suggestion is please check the altrnator replace it if required.

CHECK YOUR AIR FILTER IT SOUNDS LIKE ITS TOTALLY DIRTY ALSO HAVE YOUR GAS FILTER CHANGED IT MITE BE CLOGGED NOT ALLOWING GAS TO GET TO THE INJECTORS ALSO YOU FUEL PUMP MITE BE ON ITS WAY OUT

Check your fuel pressure, you should be at 32-35 psi, if it's too low, you wont get enough fuel to meet the demands. it could also be your crankshaft position sensor, that should give you a check engine light.

Drive shaft may be loose at differential.Just solved one of these the other day.Could alsoo be worn u-joints. don-ohio

i would have someone inspect the speedometer cable running from dashboard to the transmission

I think you mean the engine stalls or cuts out at Idle/30/60 mph.
More info wanted,as first is it a Man/or Auto ,what engine have you got 6 or v8??? When last servised by who,How many miles on the clock,dose it smoke when driving or starting ,are the revs ok on idle ,,about what temp dose it run at the 30/60 mph etc etc???
PLEASE send all info, ..
Ron.

The EGR valve is unserviceable which causes a bad or insufficient fuel control for em-missions......Hope this helps you out........EGR valves are not very expensive.

You will need to Replace the Fuel Filter and Check the Fuel Pump. Let me know what you get! Please Rate my Response, I need all the Help That I can Get! Thanks!

Have a fuel pressure test run under a loaded condition, the dealer will be able to do this.