GOOD Evening house, Siena and other gurus in the house please help me, i have and issue with my nissan altima 2001 model, when the gear 2 would want to select, the vehicle will experience a kind of seizure like you applied brake and then the gear will change like it's forced and a sound like 'kpum' will be heard.

It happen mostly when the 2 gear wants to select and most times it won't happen at all but I feel it's a time bomb waiting to explode. Because of this i got a new gear box but its still the same issue, please someone should help me.

If you have a scanner just scan the trans and clear the fault codes or take it for a scan. The problem is likely from the TCU since the symptoms is still resurfacing after gearbox change.
Am not a mechanic/electrician but I speak from the experience I had with my car.