Have these calves actually been diagnosed as having coccidiosis - Eimeria oocysts observed on a fecal examination - or did you just decide that's what the problem is?
I'm presuming your vet made the diagnosis and prescribed the Trivetrin? If administered at the appropriate dosage, it should be effective - and I always liked the trimethoprim/sulfa combinations for treatment of a wide variety of enteric diseases in neonatal calves.
Doubt that the Pepto is doing anything helpful - but unlikely to hurt anything, either.