trans fluid

[billy]

I change my trans fuild every 15-20,000 miles. Should I change sooner or is this fine? How long should I expect trans to last me? Has 60,000 miles never no problems, do maintenace as shceduled and plow snow about 8 times a year average snowfall 2-4 inches. I have extended warrenty to 75,000 or expires in October 04. So warrenty is almost up never used it cost me $2,600. So I got a feeling soon as the warrenty is up things may go bad. Any advice.