Welcome to the forum.
I assume you have no tachometer.
Roll down the window so you can hear engine RPMs better.
Let out the clutch in 1st to get rolling, shift into 2nd, after foot is off the clutch pedal, push down on gas pedal hard.
Listen for the RPMs to go up faster than the speed of truck increases, if you hear that then replace clutch, it is slipping, no there is no adjustment for that.