I went into the Allison transmission web site and found that they have a approved transmission fluid list. Amsoil is approved on the list along with several others. I plan on using this in my 2003, series 1000 Allison Transmission. What are your thoughts on using this fluid. Also read some where that Allison does not recommend flushing out the fluid. Something about getting dirt into the tranny from the back flush. One more question: When should be my first fluid change. I have 9000 miles the transmission and did change the spin on filter at 5000 miles. I tow a small car most of the time. Thanks for your help.