I have a '05 QC that when I purchased used in '07 would run in the 13.50 - 13.70 range @ 103 mph @ 14,000 miles. Now at 20,000 miles the truck will only run in the 14.50 - 14.70 range and only @ 95 mph. This is the same vehicle that is starting to show some excessive bearing wear for the miles. Does anyone have an idea of what is happening?

 

What are the 60' times, curious if that is where you lost most of it.

 

It has a K&N filter with less that 7000 miles on it. I had the trans filter changed and bands adjusted less than a month ago. I also had the fluid analyzed and everything was okay. I am using the 93 octane exclusively. I have the same tires. My 60' time in the 13's was 2.050. My 60' times now are 2.165. All times are at the same track and temperatures are not that far off. even in hot weather I don't think it shoud be more than a 1/2 second off. Even when I fried the tires on launch the mph still stayed the same. This truck has just slowed down and I don't know why. It still idles well and does not miss under acceleration. It is just slower.

 

Hmmm.... If you feel the tranny is OK I would get a compression test done on all cylinders. You can also try the typical tune up items, but at 20K miles I doubt that will equal 1+ seconds.

 

Another forum suggested I change the Rear fluid and check the spider gears. That is were I'll be checking next.

 

I followed the advice to check the rear end. I changed the fluid and replaced it with Royal Purple Rear Axle fluid and added the friction modifier. I then had the old fluid analysed. no proble with the differential. This week I went back to the track and the numbers are back on track!!!!! I guess old fluid can make that much of a difference!!!!