Gearbox issue.

[Kuldar]

So I have problem with my gearbox(1996 v8). Doesn't shift up from 2nd unless oil get really warm(doesn't happen in everyday(city) driving) and shifting from 1st to 2nd isn't smooth either. If it's on drive and want's to upshift to 3rd, then revs just go up and no load. Any ideas what could be wrong. Could it be just wrong/old oil in gearbox and needs change. New filter(which one from rockauto?) maybe. Could it be something to do with electronics? I just don't want to do oil change without thinking of other options(not cheap to get correct mercon v oil here around $100). How many litres of oil for oil change.
Thanks.

 

[alecracing]

I had a problem with my '97 where it would drive normally, but sometimes while driving it would just drop in to nuetral and freewheel. Turned out to be nuetral safety switch.

I found out because I put a scanner on it and looked at the data for the nuetral safety switch while driving. Everytime it did it, nuetral safety switch was telling computer it was in Nuetral

 

[Kuldar]

I had a problem with my '97 where it would drive normally, but sometimes while driving it would just drop in to nuetral and freewheel. Turned out to be nuetral safety switch.

I found out because I put a scanner on it and looked at the data for the nuetral safety switch while driving. Everytime it did it, nuetral safety switch was telling computer it was in Nuetral

My one has never done that, I think it might me down to lack of oilflow? or something electrical. When I'm driving with cruise on and road goes down hill for longer period, then soon it starts shifting down and ends up shifting to 1st gear. Bit scary to be honest to see revs go up quickly.