Shifting Pattern of the Plaisir Bighorn

[Mia13]

I've had a problem with my Plaisir Isuzu bighorn eversince i bought it from subic. its my shifting pattern. my rpm fluctuates when i'm travelling at more than 60kph. i've had it fixed before ( at first, when i got it from subic ayaw mag overdrive. hangang 3rd gear lang dati). when the overdrive got fixed for a time nawala ang fluctuations ng rpm. but every now and then bumbalik. and i've spent a considerable amount of money na po pabalikbalik sa mekaniko.
what happens is, when i'm travelling at more than 60kph yung rpm ko jumps ng mga 120- 250 rpm. so for example kung nasa 2500rpm at 80kph, tumatalon either sa 3000rpm or bumababa sa 2000rpm so ang nagyayari at cruising speed, umuugung-ugong ang kotse. parang palaging nagrerev ang machina. feeling ko parang hindi alam ng machina ko kung anung gear sya magshishift. parang naglalaro sa 2nd gear to 3rd gear then balik sa 2nd.
If anyone has any idea what's going on with my shifting pattern and how to fix it, I'd appreciate an email back.
Thanks.

[rheas]

Dalin mo ke joseph para madiagnose.

[attic_dude]

we have a similar problem pero sa akin medyo its a combination of other issues. maybe we can share some ideas, i've been having this problem for over a year now, pero unti unti naman ko naaayos.