94' Blazer oil question.
 

I have a 94' Blazer, motor has 45,000 miles on it. I had 10w-30 oil put in it, I was running 5w30 before. When I was running 10w-30 oil my mileage dropped in half, and my motor was working a lot harder. When I put 5w30 in it though I have plenty of power, and my mile age is actually decent. Anyone else get the same results or, is there something wrong with my truck.


1994 Blazer modifications: Performance chip, air filter, 5:10 rear gears, 700r4 transmission, 7 inch lift kit, 33' boggers.