Chugs when driving at rpms around 1300 when accerating

Could be a fuel starvation issue . Weak pump, clogged filter, restricted injectors . Does it shift correctly now ?

The 3.5 is a great engine and in the Concorde pretty efficient for sure over 20 MPG. The 3.5 HO is 1st generation and has a 10.4 to 1 comp ratio. 89 octane is required later engines after 1998 had the compression ration lowered to 9.9 to 1 and 87 might be acceptable. Scheduled spark-plug change is usually 60K miles. If plugs have not been changed than I would certainty start with them. Check tire pressure against the driver door recommended. I expect if all else is well that at 60 MPH just under 2000 RPM in over drive and smooth..

This engine was built in Chrysler's Trenton engine plant in MI and is considered one of the best power planets at the time.

before dumping more money into the car perform a compression test a weak cylinder will cause a misfire at idle that you wouldn't feel when driving

What kind of vehicle is it? Try the throttle position sensor if it has one. If it has a carburator the choke is probably not working properly and needs cleaned or rebuilt.

Does this happen occasionally after a stop? My 02' did this- brake light switch was sticking. I noticed it one night, after the car started chugging, I happened to look in the back window and saw the brake lights were illuminated for a few seconds even though i was totally on the acc.
This was a huge recall- lots of cars involved. Call a stealership and have them run the VIN # to see if you fall into the recall

Wow, you've thrown a lot into your paragraph (rpms, going up hills, chugs, dies, when it warms up, when the A/C has been on, etc). With that said, I'll try to help you with what i know and what you said, and provide you with supporting diagnostic articles.

For the engine's cutting in rpms, incremental loss of power, see this handy diagnostic article that provides you with a list and explanation of the most probable causes:
http://yourhandymanzone.com/Your_Handyman_Zone_How_To_Pages_Vehicle_Car_Zone_Cars_Trucks_Vans_Engine_System_Engine_Power_Less_Than_Expected_Normal.htm

When the car dies when it is warm and the A/C has been on, review these articles that specifically address such circumstances:

http://yourhandymanzone.com/Your_Handyman_Zone_How_To_Pages_Vehicle_Car_Zone_Cars_Trucks_Vans_Engine_System_Engine_Stalls_When_Hot.htm


http://yourhandymanzone.com/Your_Handyman_Zone_How_To_Pages_Vehicle_Car_Zone_Cars_Trucks_Vans_Engine_System_Engine_Stalls_When_AC_Turned_On.htm


Good luck!
Brad

Fuel pump or filter. I have the same problem with my 95 and am in the process of changing out the fuel pump. Already did the filter (not the problem). Hope this helps!

its probly your catlaitc converter is cloged

bad spark plug

I would start with new set of wires & good plugs that should help.