Problem after UIM Replacement

I have a 96 LeSabre with 115000 miles. I just replaced the UIM with a Dorman. I also replaced the LIM gaskets with the new GM's. Many thanks for the great info on this site. I replaced the water pump, thermostat, all hoses and did a coolant flush. The car ran perfect before the repair. I did it as a precaution. Now it seems like I lost low end torque. When I merge onto the beltway at about 30 mph I have a hard time unless I push the pedal to the floor and it downshifts very hard. My mileage seems to have gone down also. The car idles fine and there are no codes. Please help. Jim

Welcome to AF

Does your 96 have the MAP sensor that is clipped into the top of the PCV housing on the end of the UIM? IF so, check to be sure you reinstalled the small black o-ring that goes on the pcv valve itself. If not, the resulting vacuum leak can lead to many symptoms including a whisling noise, EGR insufficient flow codes and lack of power/bad mileage.