97 7.3 power not what i used to be

I have a 97 E350 7.3 with 275,000 on it for the last couple of years or so the power quite isnt what it used to be. It still runs great no weird sounds and stills pulls much better than my 96 E350 with a 351. It just doesnt get up hills or has the launching power without a trailer that it used to any ideas?

thats quite of few miles. whens the last you tuned it up? plugs,wires,o-2s,air and gas filter? you may want to stick a timming lite on it also then run some sea foam threw it after you've done all this.

in case i didnt make it clear it is a diesel with a turbo