My 2000 Dodge Intrepid was not going any faster than 35 mph but now it will go faster but it won't shift out of 1st gear. I have automatic transmission.

Well go get your car fixed by a mechanic or it something might be jammed inside

there is a computer that controls your rpm gauge, your speedo, and your shift. check that and your speed sensor. the sensor is faster and easier.

I have a 2007 Dodge Charger won't go over 35-40 mph and once you get up to that speed it jumps back and forth and when you start it and put it in gear to go it jumps real hard. My mechanic and a transmission specialist said it was a bad tranny I bought a used tranny and the used one wouldn't even shift into gear so now putting another tranny and another computer system in it. Does anyone know anything else it could be I'm so tired of this vehicle

Sorry but these vehicles are notorious for bad transmisions, unfortunately it will cost you more than the car is worth to have another transmision put in it.

Not shifting into gear or out of first gear? Engine races like neutral until trans engages? Need a better description of issue.

when in auto shift mode you place gear selector in auto shift and as you drive you are in control of upshifting and down shifting, when you want to shift up you slide shifter to the right and to down shift you slide shifter to the left, but also know that the vehicle will up shift on its own if rps are to high and will not downshift all the way back to first, and try not to take off in higher gears that nwill burn the transmission

good day, you may try replacing your automatic transmission fluid, a good run will be noticeable, hope this helps, have a nice day

Check the output sensor on the transmission,
With out a speedometer the transmission does not know how fast you are going or when it should shift

Get OBD2 codes, service transmission , check the speed sensor , camshaft speed sensor. change it, service it, check conection to wires, fuses.
Vitally

Try replacing the fuel filter if that is ok then i would sugest you change the mass air flow meter.Hope that was helpfull.