i just changed the lower intake manifold on my 98 grand prix v6 3.8 not supercharged, but im having acceleration problems, tonight ui was driving the car on the highway doing 90km/h started going up a hill, pedal to the floor and it was only driving at 80 km/h, and would not go any faster but once i get over the hill the accelerations slowely climbs up again, any ideas, please help, ive changed the spark plug wires also