I want to know if i can run 3 trucks under the same liability and cargo policy?

Yes, but your premium will go up. If you go from one to three trucks you can usually count on your premium being triple what it was with one truck. If you insure one truck for a $5,000 premium then three trucks will cost you $15,000, all things being equal.

You mean if you have 3 of the same model and colour of truck? I thought about that but chickened out. Better hope nobody checks the VIN's.