Hard shifting between First and Second gear on 2001 Lexus ES300

I have a Lexus 2001 ES300 and it has an intermittent shifting problem between first and second gear. Does anyone know what this problem is? Also when do you change the spark plugs on this model?

2 answers
Hi, Did you get the shifting issue resolved yet? Is is possible there is some software update available for the transmission control module?
Thanks!
replace transmision filter and oil