can you read the code? what code did you get?
get the upper and lower radiator hoses and replace them, when hot, they should stay firm, if not, the rubber is going. The smaller hoses you don't have to worry about too much. This is what I was told by the MB dealer parts guy.

the air gap should not be the cause of your truck dying on you, it will only cause the temp to go up. It could be the MAF, since you mentioned the airfilter was in need of replacement, it may have fouled your MAF. Scan the code and see if you get 0170, 0173 codes. The other possibility is the crank shaft position sensor.

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98 ML320 (gone but not forgotten)