Engine light came on

First of all, one thing I've learned over the years about Chrysler (and others for that matter) Transmissions is, when they start to act up, you need to get it taken care of a.s.a.p., otherwise you could be looking at a $2000.00 + repair or replace bill. In your case, whoever recommended the additive be put in there, obviously didn't do much research about that transmission, as that is not a good idea, and usually only masks the initial problem and may give temporary relief, that may come back to bite you. With that said, I guess the least expensive thing to try would be to change the transmission oil & filter, as soon as you can. When you do it, or have it done, BE SURE, to insist on Mopar ATF4 transmission oil ONLY, be put back in. Quick lubes, & a lot of Garages insist that any ATF4 brand will work, and it may, but time after time it's been reported by Chrysler owners, that they experienced erratic operation after a fluid change & it was discovered that another ATF4 brand of oil was used, and was the cause of the problem.Once fluid was replaced with Mopar ATF4, those symptoms dissappeared. I'm told your nearest autozone will scan your vehicle free, so you can try that too, and see what codes come up. Here's what I would do. Have it scanned for codes prior to fluid change & write them down. Have fluid & filter changed, clean all electrical connectors to transmission, and have codes erased. Then try driving it for a while to see if any codes or symptoms re-appear. If they do, have it scanned again, and attend to the problem area that the code refers you to a.s.a.p., especially if it is transmission related. Make sure while servicing the transmission, they or you, take the time to remove all electrical connectors to the transmission and clean all connections good with contact cleaner or similar electrical cleaner, as quite often, a problem can be narrowed down to a bad or corroded connection, but it is the last thing they check.
Good Luck, and keep us posted.

Do your brake lights come on okay?(the switch also controls your trans!) the engine light ALSO warns you of trans prob's!! get it scanned NOW by a good shop!!(not the local auto parts store!) "sounds"like a bad selector switch,or valve body ,on,and,in the trans. maybe worse!!
PLEASE have the car scanned!,the light should NOT go ON AND OFF,unless your getting VERY bad gas!
any way you look at it,when the engine light comes on,the comp stores the "error"so scanning should reveial the prob!(please dont add stuff ,it just makes the final repair more expensive!)