Ours have been like that too. I switched one box off for a minute last night and that cured it. I've had to turn them off about once a month or so to cure the slow downs and freezing. But recently it's got worse.
Don't know about you but I'm getting a bit fed up with TiVo and have been looking at getting sky Q later this year.
My tivo's speed is usually acceptable but I have noticed that at peak times 7.30pm 9.00pm 10.00pm it does slow down quite considerably. Why should this be? I can only assume that at these times there is extra demand in the traffic of information to and from VM. This I think is what the forum team euphemistically call a 'utilization' problem and until their network infrastructure is supplemented and upgraded will be likely to persist. Most tests and visits by box fitters are, from what I can tell, ineffective but it is hard to be definite as most 'solutions' are hidden behind private messages(pm's).