[x-sno snake]

Do the transmission oil changes and other maint. first. A number of things will give you the CEL and TC lights. You are well into the egr valve "set the lights" mileage. Any shudder at cruise, light throttle setting in the 50-60 mph range? Do a "search " on egr and any other symptoms the van may have.

A lot of things can set those lights and just about all are a lot less expensive than a tranny.

Good luck.