Car behaves differently after mechanic

Bit of a strange one, i recently had to take my 2002 Mazda tribute to the shop
twice in two weeks, once for an oil change, coolant flush and new tires, and once
for a new water pump (problem uncovered by the coolant flush)

Both times, the car has behaved very strangely for about 24 hours after  - the revs
have been inconsistent and the car seems to lurch a little at low speeds, plus it
seems to struggle to change gear at the right time... the odd thing is, each time
this has happened, it has then gone back to normal after about 24 hours and has
been great after that

im just curios as to why this may happen?