gas tank pressure

[6768chevylover]

I just got back from a long 211 mile journey to a car show in this nice hot weather were having on the east coast. Found out my speedo is off and that apparently I get major pressure in the gas tank. I drove down to a show on thursday and the temp was around the late 70s early 80s, had no issue.. Went back home yesterday and the temp was almost 90, issue.. I stopped at a gas station to get gas. I had about 1/4 tank left. I open the cap and gas and pressure spit out. It was all highway speeds for both trips. Its a 71 blazer, replacement tank, no return lines, vented to rear tank canister, and tank filler line is kinked a little. I've never had an issue but then I never took it on a long journey like that in the hot sun at constant 70 mph. Any ideas or corrections?