1997 minivan codes P1870 and P0101

hello my van had over heat and shut down every 2 mile so I had replace the water pump and thermostat and still doesnt fixed so i took it to the auto repair shop and they told me it was the manifold gasket so it going to cost me $590.00 to replace it. I said ok so next two day they call me and said it was ready so i had went down and pick it up and drove for 4 miles and it over heat again and shut down i call the auto repair shop and they told me they will towed it back to their shop without any charges. so they had it for another day and call me back next day and said it was the head gasket it will cost me $1300.00 and they will refund the $590.00 back so i told them no dont touch it and i will have it towed it back to my housed and that they have to refund my money back for guessing. so i was luck they refund my money back without any problem but he was mad about it. so once the van was back at my drive way i did a back flush on the raditor and test it still same problem so i went to auto parts store and bought me a $10.00 head gasket sealer and work on my van for a whole day next morning i fill the raditor up with antifreeze and drove it for 90 miles and it doesnt over heat again keep my finger crossed and next day i drove for about 125 miles still doesnt over heat. :) now i have the service engine light came on as before when all this was happening then i went to murry auto store and rent the diagnostic tester and i have these two codes P1870 AND P0101. Can anyone tell me is this an easy fixed and how much parts going to cost? what is the problem for the code?

is the code p1870 mean:
P1870 Transmission Mechanical Transfer Case 4x4 Switch Circuit Failure
my van is front wheel drive not 4 wheel drive>

It means the pcm has detected some type of internal trans slippage and has boosted the line pressure to try and compensate, lots of site and google info on this do a search. Many things can cause, this all are internal in the trans. 101 refers to an issue with the maf, a vacuum leak or bad wiring connector to the maf.