welcome to the forums
think you'll fit right in
think you're being a bit paranoid here... naturally speedos post a higher speed anyways (allowed up to 10%) and logically it isn't worth the dealer's time to tamper with something like that...5 mph over at 200 hours of driving is only 1000 miles which is like 10% of total miles if you drive an average of say 50 mph..would be a pretty desperate move with very low return
as far as "lag" on the speedo, I'm assuming you're using the digital readout in the tach...hope we're on the same page it will skip over numbers..so you're saying you come to a 100% complete stop and it doesn't register 0 right away? think might be part of the paranoia
that sort of service story is common..either do it yourself or find a different dealer. turnover is pretty high, maybe they'll have more caring techs next time