1999 Ford Windstar one problem after another

When i first bought my ford windstar, (I bought it used) it was wonderful, used it alot for traveling, had no problems until just the past year, the heater stopped working, possible actuator, typical problem with this van, had the converters changed, they were plugged, resignator was also changed, the engine has a bad skip in it, we thought it was the transmission, but they keep saying its not, the engine light is on, we have changed just about every sensor on this van, the last 2 to change is the map sensor and the egr valve, when taken to autozone they kept telling us it was one thing then another come up on their code reader, im at the end of my rope on this van, and oh yes i had a full tune up done on it just 3 months ago, no change in the engine performance, sucks gas like crazy, and it still skips like crazy, it also runs really rough when it idles and sometimes shuts down for no apparent

reason. any suggestions???? please let me know!!!!