Truck moves fine in reverse but won’t move in drive it is an automatic transmission
Model?
Model year?
Odometer mileage?
History of transmission maintenance?
Current level, odor, and color of your trans fluid?
It sounds to me like your transmission is going to need to be overhauled, but until you provide answers to the items above, that is just a WAG.
WHAT truck ?
Parking brake ‘on’ ?
“Parking brake ‘on’ ?”
Sounds like a parking brake to me as well.
Last time that happened to me it was transmission overhaul time.
So “D” works the same as “N” then? You can tell no difference whether the transmission is in Drive compared to Neutral? hmm … well, you might get lucky, could just be the linkage between the shift lever and the transmission is amiss. Have you tried other shift settings besides D, N, & R?
To eliminate a sticking parking brake as a possible cause, ask your shop to jack up the rear end and make sure the rear wheels spin freely by hand with the engine off, transmission in neutral, and the parking brake off.
One of the most common failures experienced when an Automatic goes out to lunch… Sometimes it can be something silly and an easy fix… Other times…nay…most times…the trans is donezo.
One of the primary reasons I still cling to the stone age manuals… In fact Manual or Auto is perhaps my biggest decision maker on whether to buy a vehicle. Its always a crap shoot with Autos esp over 100K…
Maybe it is just me, Blackbird, but I’ve broken 2 manuals on street cars (don’t ask how many I’ve borken in race cars) and no automatics. One locked in 4th gear and the other blew out the case the 3rd had a bearing go bad in the Powerglide-like overdrive tacked onto the back of a T10 4 speed (Corvette 4+3 tranny). But I have owned way more manuals than automatics so the sample is skewed.
@Mustangman methinks the problem isn’t the transmission…but the Nut Behind the High Horsepower Wheel… 
Something tells me you have more power than most under your vehicles hoods. LOL
Well @VDCdriver is a 98 chevy z71 3500 with a rebuilt 350 engine it has about 250000 miles but only about 100000 on the new engine the transmission has had a problem like this before but it always got better once it was warmed up 10-15 minutes the truck is a 4x4 and is usually well maintained but has set up a couple months I have tried 1st 2nd and 3rd but it won’t pull forward in anything but reverses it moves fine and the parking break was not in use and the linkage is fine it just don’t sound like it shifts into gear.
You need to get it towed to an independent trans shop with a good reputation.
I would anticipate that it needs to be overhauled, but you should allow the professionals in that shop to give the specific diagnosis.
Have it towed to a reputable independent transmission shop for an evaluation. I recommend against a chain operation, as they’re usually focused on revenues above all else… and sometimes even in lieu of honesty. Sometimes the technicians are even bound by quotas and/or even on commission for all work they generate above a specific minimum.