Blown head gasket?

[Russco]

I have been fighting this for a while now and thought I had it fixed but it's still acting up on long trips. This weekend I drove about 2 1/2 hours (@ 60-65mph) with the temp about 190 then I smelled coolant being puked out the temp then dropped to about 180. I knew something was up, so I stopped at the next exit. The temp spikes to 240 I topped it off (11/2 gallons) and it was fine again for the next 100 miles to where I was headed. I've noticed if I run faster than about 65 it will do it and it always takes about the same 11/2 gallons to top it off. I can drive it around town for weeks and it won't get hot or purge Any coolant only on the highway and if I run faster it will do it sooner. It holds pressure when tested, doesn't smoke, runs fine , no oil contamination. What do you think? My other thought was that maybe the radiator is somewhat restricted could the pumps build enough pressure to force it out the cap ( the cap is new and correct length 7psi). Edit: I didn't mention this is a stock 8BA in a 51