the best way is to use a block tester. But some things you can check is for coolant in the oil ( it will look like a milk shake). Check compresion to see if you have a loss between cylinders.......
get a compression tester tool from autozone. screws into the spark plug holes.
warm engine, remove ALL spark plugs at once, burn hands on headers, curse, thread the tool into the first port, hold the throttle to the floor, crank the starter and let it spin over 2-3 times and record your reading, repeat for the rest of the cylinders, and report back your findings.
With engine warn, Remove coil wire so car wont start. Remove spark plug from 1 cyl at a time. Screw in compression tester. Hold throttle open and crank engine until highest reading is reached. All should be with in 10% of on another.
The block tester is the best method, can be pick up at NAPA.
Also check for overheating, perculating bubble in overflow bottle. Purging from overflow bottle.
a blown headgasket cannot and should not be driven on. You'll get water into your oil, blow out your connecting rod bearings...if you're lucky. if you're not lucky, your cylinders will fill with water, you'll hydrolock, and blow up everything. at the very least it will run worse and worse and worse.
I'm just making sure because I'm trying to see what can make my car performanc be off because off every thing I have on the car it should be better mane a bernd valve our what else should I look at.
It sounds like it has a big vac leack it has new header gasket it pull hard at take off but the top end its not ther I have every thing that's in my sig .
lol, you have no sig. tell us all of your mods, next pick up a vacuum gauge and check your vacuum, you should be 18-20 pounds or so if you have a stock cam. are you speed density or mass air?
you're pulling at straws. 5.0's just don't blow head gaskets unless you have a problem with your boost or you've overheated it ten million times.