Loss of power & mileage after towing...

I recently pulled a trailer with an old Blazer for about 2 hours. About 9000 lbs total weight (truck, trailer, and blazer). Now I have lost quite a bit of take off power and my gas mileage is down about 2 MPG. Any ideas what could be wrong?

'01 Silverado 5.3 Ext Cab
K&N Air Filter

After working hard like that it is possible that it now is in need of a good tune up. Spark plugs/cap/rotor/wires/fuel filter.

Changed plugs and wires 2 weeks before towing. Changed fuel filter 6 months ago. I used the tow/haul mode but I wonder if maybe I damaged the tranny somehow.

I misread that , i thought you were towing with the blazer, not towing the trailer with the blazer on it. If i do a little math , my 88 K1500 jimmy (same as a full size blazer) was 5,600 lbs roughly, my 2000 silverado ext cab it 6,400lbs roughly, that is 12,000 lbs not including a trailer of anykind.

ext cab silverado's don't even wiegh in at 5000lbs ..... mine wieghs 4860lbs just last week

As for the weight of my Silverado, i looked at the tag wrong :screwy: , 6400 lbs is the gvwr. But i know for a fact that my 88 was 5600 lbs cause i weighed it at a weigh scale.

The Blazer was actually an S10 Blazer. Not sure what year. My Ext cab weighs about 5800 pounds. Figure 1200 for the trailer and another 4500 for the S10 Blazer so roughly 10,000 pounds. A 5.3 extended cab should be able to handle that, and it did. But now I have lost some power and take off speed.

how long ago did you pull this load and how many miles have you went since then???

Pulled it March 19th. 130 miles one way. Pulled unloaded trailer back. Round trip 260 miles. Top speed 72, average speed was 68. Since the trip I've gone about 750 miles.

Might get it scanned to see if anything went on.
On a similar note, my friend pulled a backhoe on a gooseneck with an '04 1/2 Dodge Cummins 4x4 and because he pushed it so hard(truck has a chip) the motor burned a hole in the piston. He said the truck was blowing white smoke under acceleration afterwards. I don't think this your problem, but I thought it was an interesting story.
Jeb