Engaging 4x4 Low...grinding gears

I am in the process of purchasing a '95 K2500 454. It's had some transmission work recently and seems to be running great. However, when I moved the shift lever from 2H to 4L I have to do it fast or the gears grind...the same with moving it back to 2H. (Going from 2H to 4H and back is no problem...just when moving through neutral to 4L.)
I talked with a mechanic a the dealership and he said that they had an update kit (?) installed when the transmission work was done. He said that normally the rig has to move forward to before the front wheels actually engage but with the update kit they engage instantly...causing the gears to mesh...if you don't shift quickly (jam it from 2L through N to 4H) then you grind gears.
I don't know...but this doesn't sound quite right to me. I had a '95 Yukon and didn't have the same experience...but then I didn't have this update kit.
My concern is that something wasn't done correctly when the work was done and I want to make sure it is fixed before I complete the purchase.

Any knowledge of this update kit or similar experience when engaging 4L?

doesn't sound right to me. grinding gears is always a very bad thing.

If it has an automatic, the trans. should be in Park when shifting between ranges. Otherwise, the trans. output shaft will turn when you shift the transfer case through neutral, causing a grind when you attempt to engage high or low range. This will occur even with the trans. in neutral.

I will have to try this...it seems to me that I tried to shift when in park but couldn't get the shifter to move. I figured that this was for anti-theft so that it couldn't be put into neutral and towed away...but, I will try again.

Anyone else with some thoughts on this?

When you shift from H to L you can't be moving. You can be in either park or neutral.

You can't have a load on the rig. Like sitting on a hill. The best way it works is to, come to a complete stop, put tranny in nuetral for a second, with foot still on brake now put tranny in park. Do not release brake. Shift T-case wherever you want. I don't know if I explaind it right. I guess what I'm trying to say is that you can't have a load from the wheels or the engine coming into the T-case. Also some of these transfercases have a sycro ring and some don't.