after about 10 mins the engine is starts knocking a little bit and it pulls alot slower than normal this is on a 97 5.0 running 92+ gas no mods execpt air box please Help

I have the same problem so PLEASE respond because its been driving me nuts lately. Is it typical of cars with high miles?

Have you cleaned the MAS? Changed the fuel filter? Maybe your fuel pump is crapping out.

Check under the truck to see if you might have a fuel line near a exhaust component . If so it can heat the fuel in the line up and cause it to boil thus reducing the power . Might be something up with the O2's and or fuel pressure regulator .
Id make sure to check your engine temperatue also , the thermostat could be stickin and the enigne running hot .

i agree with what they said. check your fuel lines. my 92 has about 160K miles on it and it still runs great.

The fuel lines are run on the driver's side and the exhaust is on the pass side. That's not the problem.

Reset your ECU by disconnecting the battery for 10 minutes. Reconnect the bat and start the truck, let it warm up to normal operating temp and turn on the A/C for a minute or two. Then drive it around for about 20 miles. Don't take it out onto the highway and cruise for 20 miles at 80. Go in stop and go traffic. This way the ECU will relearn the fuel mixtures required.

If it still persists I would take it to a shop you trust.

On a 5.0L the fuel line is close to the exhaust on the drivers side of the truck up at the engine :)
I doubt it is the problem but it is a check . If somehow something got bent the line could be close . There is a bunch of stuff that could cause it to happen and most are simple .
At NADC they taught 1 golden rule ...........K.I.S.S.

Keep it Simple Stupid .

I try to live by that when Im repairing vehicles , as most times it is simple .