Look for worn / loose parts under the dash. I've had to replace bushings, the arm that connects the pedal pivot shaft to the clutch master & in one instance the big aluminum bracket that holds up the dash ( but that was on a '87 -'91 era truck ).
The 92+ isn't supposed to have that problem, with the pedal assembly falling apart.
It could still be a worn master slave or sticky throwout bearing or pilot
With the m5 sadly you have to drop the trans to get to the slave throwout or pilot.
If it were any of those though, it would start in neutral.
I would look at the clutch lockout switch, and then bypass it unless you have kids that might be messing around the truck.
Not sure about the 5.0, but the 4.9 with a high torque starter will fire up and take off in gear.
It should also prime up in 10-30 seconds and then shut off.
If it doesn't shut off you will need one of three things, fuel pump relay, eec relay or a new eec.
Mine turned out to be a fried eec. I drove the truck for over a year with the pump never priming and shutting while on accessory, had no idea it was supposed to till the computer went.
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