Goes into limp mode when decelerating at highway speeds.

It's in limp mode. Continuing to drive highway speeds in second gear is going to destroy the transmission. Limp mode is incorporated so that you don't drive very far or very fast, but just enough so you can get it to a repair shop. The longer you drive it, the more it's going to cost - up to the cost of a new/rebuilt transmission.

the output speed sensor is going bad,or may have a broken wire on the connector.repair r the wire if so,or replace the sensor.Transmission goes into limp mode to protect it'self,and engine,from internal damage. repair this,and you should be good

sounds like a fuel supply issue or it is in "limp home"mode due to a ECU or sensor issue,is the engine check light on?

Use a bottle of yellow HEET dry gas to remove any moisture problem in the fuel.

Clean / replace air filter.
Check ATF at level ground. Top off ATF to MAX level.

check your speed sensor output with a scanner

check engine codes. if it goes into limp mode it will store a code. probably a tranny problem

sounds like your egr valve is opening too far at part throttle and sticking open. it is actuated by solenoids that open and let engine vacuum in. you were on a good path in checking the vacuum lines. however this may require replacing the egr valve and gasket. the egr valve is circular in shape on top and usually is bolted down with two bolts. its located on the engine side facing the firewall.

I would start with plug wires rubbing on something and created a short.and is not compleatly worn through. a cheep place to start. good luck with it.

Of course the first thing to do is to check the transmission fluid level. Next have car scanned for codes, if there is a speed sensor malfunctioning, the transmission would go into limp mode. In limp mode, only reverse and second gear work. Many auto parts stores will scan your car for free. I hope this helps.

this is called "limp mode" which means to "limp" home. Chryslers default to limp mode when there is a problem with a speed sensor, body control module or other sensor

scan the computer and see what it says

I sometimes remove a bettery terminal leave disconnected for a few minutes and this resets the computer and clears codes

better to scan though and clear and see if it helps


jon