Roll the carpet back in the front footwells, a task made more do-able with a little determination and removal of the seats, dry the area as best as you can and then dust a little talc or French chalk on the firewall and over any of the transmission tunnel you have revealed.
Start the engine and watch for any tell tale drips/rivers etc.
If all clear but carpets were found to be wet turn on a/c and watch for similar signs.
Also check apertures through firewall as perished gaskets and grommets will soak your carpets and rust your truck from the inside out!
Next test is to visit local garage and ask them to check that you don't have a head gasket failure, they just check your coolant for traces of combustion products so don't let them rip you off!
