Stalled and need advise

[6eight]

I came across a recipe using corn syrup and honey and wanted to give it a shot. I recently got a 24 gallon stainless fermenter so I also changed my batch size. According to the calculations I used 4 gallons of corn syrup and also added 5 lbs of honey with 20 gallons of water. My starting gravity was 1.08. That was right in the range of the recommendation for the recipe. It has been over three weeks now and I'm sitting at 1.035. I ferment in the shed and my worries are the 90+ heatwave may have killed the yeast. I added some nutrient a week ago when I was at 1.04, but I haven't dropped much. I used distillers yeast which I have had for about a year now. It has been kept wrapped in the fridge and seemed to start just fine. I don't want to lose the batch, but I don't know if I should add more yeast, take if off the current yeast and start it again, or just pitch it? It doesn't taste sweet, but it also not dry either. I have a thermometer in the shed and it has fluctuated between 75 and 90 (night and day).