Please done let this freak you out, but simply expand where you are looking for a solution.
I wrestled a problem similar to this very recently. Mine was a combination of stuck brake caliper (diagnosed by hot wheel) and air in the coolant system. While these things are capable, they aren't powerhouses. The increased load by a bind in your drivetrain somewhere coupled with a cooling issue is sure to cause issues.
Also, just out of curiosity, did you test your new thermostat before you installed? I've read quite a few posts about faulty aftermarket thermostats.
Good luck brother and have a good one!
