Truck has been running 100% fine - no problems.

Then, a week ago, it stalls as I'm coasting. It starts right back up, idles fine, rev's fine. I put it in drive, step on the throttle, and it sputters and stalls. It doesn't sputter like I have a bad plug or wire - it sputters bad - then it stalls. It always starts right back up, idles great, rev's smooth.

So I'm thinking to myself, it only stalls when the engine is under load - so I put it in 4-Low, shift into drive, step on the gas, no problems. It will run out across the parking lot through all gears, no sputters or stalls. To me, it seems like a bad coil - so I have it towed, and the mechanic seems to think the exact same thing, so I'm feeling positive.

He says he checked it out, the spark was really weak, so he changes the coil, took it for a ride, and reported it was fixed. I paid him ($115 for labor and a coil) I drove it for a week, including hauling a big load of wood up and over some big hills at highway speeds, no problems. Last night, the same issue starts again. I limp it home, but now I can't figure it out....

Seems like fuel pump is ok, since it starts, idles, revs fine.
Coil was just changed.

What can I check now?

Pete