According to some sources, the contract between Spike TV and RTM expired and initially Spike TV decided not to renew.
After seeing the huge ratings fall the first few weeks of December they have seen the error of their ways. So starting on Sunday, January 5, 2014 Spike TV will have all 4 shows under the new name and format:
Powerblock is now PowerNation; Extreme 4x4 now becomes Extreme Off Road; Horsepower is now Engine Power; Trucks is now Truck Tech; Musclecar is now Detroit Muscle.
Only on Sundays you can watch all four shows twice, CBS sports will air them from 6-8 AM ET and Spike TV will have them from 9-11 AM ET/PT. Spike TV has renegotiated with RTM productions and they will air the new shows, but only on Sunday mornings.
You can check PowerNation's new schedule and what network the TV show will air on here.