I bought gearboxes for the pz3 tank from Asiatam
Engines is designed for PZ3 or Tiger, I have Torro metal PZ3 - that is, twice as lighter than a tiger and these gears are not able to move this tank.
I think it is the fault of the weak engines that you installed in these gears
I specifically tested these gears for torro and elmod. The same problem. Gears have a problem to drive half

I wrote to them what they think about it, but they do not see too much problem in the operation of the transmission.
As you can see they are at most suitable for driving full-plastic Heng Long tanks
On Monday I will ask PayPal for a refund of some costs - I need to buy larger engines and larger planetary gears to get it started
I attached the video: