ok. you can also try Dwarf's suggestion by using different Brand disc. Some cheaper ones are CR** and don't work at higher speeds. If the problem still occurs with various disc at high speed then it’s either a hardware or software issue.
To rule out the software or know if it’s the problem you can:
1. Check your burn setting. Buffer, disc-at-once , track at one, format, etc.
2. Try different softwares. Some softwares don’t like some drives. I recommend not installing all at once. That may land you in more problems
3. (Personal preference) I don’t like burning software that "steps on the gas" 0 to 24x in 3 secs, no. I think the best designed software slowly increases the speed of the disc.
So, check these out, and if the high speed is still not working you may have a hardware issue