lack of power

[fordboy010]

I have a '99 7.3 late production model that has a lack of power when towing heavier loads.

Started out, I was towing a boat down the interstate and could run 75+ if I wanted to. I stopped for a quick bite and when I got back on the road I couldn't get over 70. And when I hit a hill, it killed any speed I had. I did have a guy run a scan and it did have 1 code. I believe it was 603? He said something about a keep alive code. He said it was probably from a chip being installed by previous owner. The truck has no chip now and is bone stock. I did pull the airbox intake and take a look at the turbo. Should it turn freely or not? Any help is appreciated. Thanks.

BTW, great site. Lots of helpful stuff.