Don't know about T34's but I was always of the understanding that the Panzers were diesels, one of the (many) reasons they had an advantage on the 'Merican tanks in combat - they tended to not explode when hit like the "Tommy cookers" did.
Nope. The Panzer's along with most M4's burned gasoline. Armor at cosine thickness (on the hull, the panzer's turret has always been a weakness) between the two tanks has a difference of a mere 5mm. The difference is that the German
panzer's (well, the Panzer IV at least) had been carrying the KwK 40 since mid 1942, while the Allies didn't upgun the M4 untill July of 1944.