Classic ZF auto box problem?

Hi hope someone maybe able to help. The other day i was trying to reverse a car trailer with a car on up our drive. The 1st part of the drive has a small incline and the rangerover was in low box reverse, i had nearly got the trailer to the top of the incline when the car refused to go any further backwards. i had to unload the car off the trailer before the range would continue to move backwards. I want to know if this is a terminal problem that will require a box change. The gearbox is not the origional but was 2nd hand, however i did put a brand new torque converter in. It moves fine in the forward gear but even unloaded it seems sluggish and a bit unwilling in reverse. Any advice would be greatly appreciated.

check oil it will be blackish id imagine ,sounds like clutch pack burning out

oh bugger that sounds terminal! thanks.

they are fixable just depends on total condition and capability of mechanic

The clutchpack failed in forward drive in one of mine....

It was easier for me just to find a good replacement box.

Thanks, i do have a replacement box but was hoping i wouldn't have to do a box change now winters here! oh well.

it always happens in winter, normally in rain or snow

I had to have one re-built on my old 4 door in november and then the heater matrix blew in the snow the following year :doh: the headgaskets started to go in feb and it was ebayed in march