Starting problem after highway driving

[terryggoround]

I'm having a problem with my 1970 gmc jimmy. A little back ground info- Jimmy have a brand new 350 crate motor from GMC it's a 5.7Lt with a mannuel 4sp tranny and is a 4 wheel drive. The motor has less than 500 miles on it and the issue is after driving on the freeway for about 30 minutes when I turn off the the engine it won't start. this has happened 2 times the first time I thought I might be out of gas (fuel gauge not working-yet) and I was at a gas station. It sounded like it wasn't getting fuel(also has brand new fuel pump and the fuel hoses had all been replaced). it was dark outside and I took off the air filter hoping I could see if the carb was getting fuel. I could not see all the way in carb but could smell the gas very strongly. Then when I was putting gas in truck I could smell the gas fumes and when I tried to pump the gas in it spit it back out at me. I thought ok maybe this is some kind of vapor issue. So I very slowly pumped in about 8 gallons all this took about an hour and when I tried to start the engine it still sounded like it was not getting fuel but it did start and ran fine. I did notice when I got home the smell of gas fumes from both exaust pipes at the rear of truck. Also the PO removed the charcole canister. I have check the gas tank and hoses for leaks but can't find any.
Thanks for any help for a rookie.