1996 Dodge Grand Caravan LE

I’m having a problem with my van. When I first bought the van it ran but the tranny had 6 things wrong with it and wouldn’t go above 35. It was in limp mode. Then I bought a 99 transmission because someone told me it should work. Well I got it in and now the van will start but wont stay running. The cooling fan comes on but then won’t idle. Codes for the map sensor and cooling switch come up. I’m lost now. I have no clue what to do next.  Any help would be appreciated.