hot gage poor heat

If the problem was your thermostat, you would still have some heat. So, likely, that is not the issue.

If you have just had your radiator flushed, then perhaps it was not refilled properly. Some vehicles, especially newer ones, have a 'procedure' to refill the cooling system. Some shops will wave that off and just return your vehicle. Your owners manual will have information on this. (Hmm, my idea of 'newer' is getting older. Sigh. :)

Another possibility is that like most cars, the controls you adjust are vacuum operated, and there is a break in a vacuum line.

Without knowing more details, it is hard to narrow it down.

Details like:

Have you had it serviced recently, and what was done?

Does the van have any other problems that started at the same time?

Except for not having warm air, does the ventilation system function as expected?

....

Tonka