Sole F80 Belt Lagging Problem

We purchased an F80 last January, replacing a Nordictrak that we'd had for 22 years. Treadmill is OK, but when speed is increased, when like walking 2 or 3 mph, there's a lag before the speed catches up to the new speed. Belt is lubricated well and bed is clean, whole area around treadmill kept clean, having a problem trying to figure this one out. Also, when speed is decreased to very low speeds, like .5 or .6 mph, belt barely wants to move. Haven't contacted Sole yet, thought I might get some ideals here. The treadmill is OK, but OT, had I to do it over again, I'd have had the Nordictrak repaired; only thing I'd had to do to it was replace the belt once, really sure the electronics went out on it, just happened at a bad time when the pandemic was still affecting things, making repair parts and service difficult.
Oh well, we're making it fine with the Sole, but I can't believe they can still advertise 3.5 HP for the motor (no way ).
Thanks.