Stuck lifter

So I have a 09 5.7. CM runs great driving around town. If I hit the highway and run at highway speeds 65-70 MPH. After about 20-30 minutes into the trip I can hear what sounds like a stuck lifter sound coming from the driver side of the motor. When I get to where I’m going and slow down to street driving speeds 35-45 the stuck lifter noise increases. After I stop and spend some time out of the truck hour or two. Get ready to head back to house starter her up sounds great. Short while in to the drive the stuck lifter sound comes back.
What could cause a lifter to act like that.
Most important what is the fix.
Thanks
Jim

 

Are you sure it's a lifter?
Kinda sounds like an exhaust leak/cracked manifold

 

You can run a quart of ATF with the oil for a little while a few times to help. The strong detergents will clean up built up varnish in the engine. Pour it in, drive it for 30 minutes, then change the oil. Run on oil for a few thousand miles, then mix again and drive it for 30 min or so followed by an oil change. Report back and let's hear the results.

 

How would an exhaust leak or cracked manifold just make that sound intermittently. Would it not always have a leak.

 

When the manifold heats up it expands enlarging a crack or leak. Just a thought
The ATF in the oil is a good idea

 

I have been on the road. Thanks everyone for your input. I’m going to try the transmission oil treatment when I get back home this weekend.