have a 2001 XTerra 3.3 engine with auto transmission. It has 182,600 miles and I have been experiencing a transmission lag in engaging drive only first thing in the morning. After it engages once in the day it will drive fine. This has ben going for about two years but recently the lag time has increased from about 5 seconds to 20 seconds. I did a partial fluid replacement about a year ago and it made no difference. The fluid seems clean and in good condition. I have heard Nissans suffer from this, what is the cause and what would be the fix?