Hi Cubguy, what type of fertilizer are you using?

Once a pumpkin plant is developing fruit, a fertilizer high in potassium is helpful (if you're not sure look at the back of your fertilizer for the n-p-k numbers, you want the k to be the highest) Definitely stay away from anything high in nitrogen at this stage (the 1st number).

I'm not an expert but I know that really big pumpkins need a lot of fertilizing, you may want to increase the frequency of your feedings. If you're worried about burning the plant, there are a lot of organic options that won't burn.

Could also be that the female flower didn't get pollinated the fruits will shrivel and die.

I would also back off on the fertilizer and if you can get some fruit to set thin the fruits to no more than two per vine as the plant will put everything into them and I would only water every 3-4 days unless the plant is wilting