cooling question possibly HG blown?

[Novacaine]

I have a 86 T stock bottom with champion GN1's 212/212 tappet pt67 60lb inj. 160 themro etc.
I have a kinda strange problem as long as the car stays under about 1500 rpm the temps stay from 165-168 if the rpm goes above 1500 for over about 30 sec the temps start rising slowly and ive seen them get to 195 it takes about 5min or so for it to get that hot,at which time i stopped beside the road and let the car idle to cool it back to 165, took about 5min. Ive checked the fan works fine and it has a griffen rad brand new so i dont think its any of the coolant system at fault, only thing i can come up with is possibly a HG what do you guys think? Im goin to run a compression test tomorrow and hopefully that will give me somewhere to look.
Oh almost forgot it does still have the stock fan on it.

 

[Mike70gtx]

Mine just did that, but my temps would go higher. If it's a headgasket, then there is a good chance you'll see boiling in the radiator resevoir.

 

[84BuickGNYorkPA]

Do you have a front mount? Do they climb any higher then 195? I just made a 250 mile round trip yesterday and mine went up to 200 but mostly stayed at 190 area, but I have a RJC mega cooler and a stock fan/radiator. It's hotter than I like but just so temp doesn't keep climbing (95 deg. yesterday) I was ok with it. Remember that the stock thermostat is 180 deg.
Chuck

 

[Mike70gtx]

Depending on outside temp, running a/c, etc. 195 is not "that" hot. Does it seem like it would continue to rise over 195 or does it hold there? High stall convertor or slipping tranny can produce some extra heat also. My headgasket problem would cause my temps to go up after I applied some boast.