2000 express with a 4.3 vortec engine

quit running last night got on the highway push down on the gas pedal when it got to 50 mph started shuddering and wouldn't go any faster till I let off the the gas pedal and it slowly climbed up to 70 mph seemed o.k. after that stopped at a store and when I came out engine cranked but would not turn over. has only 64,000 miles on it. think maybe the timing belt jumped and time is out. Is the motor a interface or interference motor where the timing belt breaking or jumping could do serious valve and or engine damage??? or a non-interface or non interference motor which could mean a easier less costly timing belt replacement???

quit running last night got on the highway push down on the gas pedal when it got to 50 mph started shuddering and wouldn't go any faster till I let off the the gas pedal and it slowly climbed up to 70 mph seemed o.k. after that stopped at a store and when I came out engine cranked but would not turn over. has only 64,000 miles on it. think maybe the timing belt jumped and time is out. Is the motor a interface or interference motor where the timing belt breaking or jumping could do serious valve and or engine damage??? or a non-interface or non interference motor which could mean a easier less costly timing belt replacement???

No timing belt on them.
Got gas in it?
Can you hear fuel pump prime up key on?
Check for lose of fuel pressure or good hot blue spark to all plugs.
Was any check engine lights on?
Post back fuel pressure reading.