That’s exactly what happens with the seat belt not buckled but he says the seat belt is buckled. There is another connection under te seat that may be loose like Ebwhite said check for cut pinched wire or backed out pin. Very strange that it’s both units. FYI only drivers seat has the belt switch.That's interesting, wouldn't you think it'd be throwing all kinds of codes being starved of air so much that it only goes 10 mph? I mean it'd be so rich that it would be backfiring in the exhaust don't you think? I mean I understand the mass airflow sensor adjusts trims for fueling, but the base tables are still there and they just get tweaked with the values of the incoming air. At least, that's how it's worked on other engine management systems I'm familiar with. Maybe these are different?
Either way, it's super weird that both machines have exactly the same symptoms.
Maybe someone with a pro r can go drive without the seatbelt and see if it's the same speed limiter...my gut still says it's related to that.