Hello & Welcome to JA,
From what you have said ,it does sound like a possible catalytic converter , if top rpm is 3000 & top speed is 10-15 mph.
To check a converter for restriction ,remove the engine 0/2 sensor. Install a low pressure gage in 0/2 port. Start engine & run at 1700 rpm,look at gage. If the gage reading is more than 1&1/2 psi , the converter is plugged.