Don't know what adapter you are using but I have not had good luck at all using the small RV30A-15A type adapters like these...

I always use something like this RV30A-15A long dogbone type adapter (WALMART)

I also use a 10-gauge (10-3) 50-foot extension cord when connected to the garage. I have used the 12-gauge size (12-3) but would never go smaller than that. Small gauge extension cord have too much loss
I always keep tabs on my connections when being used to prevent the 30AMP Shore Power Cord from looking like this photo. Mine run cool to touch...

Roy Ken