loss of power

[wifiabc]

After the mechanic changed the valve cover gaskets and distributor o-ring recently, my 92 windom(ES300) drives differently. It's not as powerful and responsive as it used to be. It also seem to accelerate slower and revving at higher rpm when starting from the traffic lights.I notice that the rpm is about 2000rpm at 40km/h (24mph) and 2500rpm at 60km/h(38mph).

What are the possible causes with these symptoms? What should be the normal rpm at which it shifts gears?