Someone told me that may be too high and some DVD players can't handle that bitrate. He recommended I try 4000 which I have been using for some time.
You've been misled.
Most dvd players can easily handle 8000kbps, and only start freaking out when bitrate peaks over 9000. I regularily set max at 8000, average at 7000, and min at 6000, using VBR 2 pass.
Your GOP settings should be fine. Some players MUST have a closed GOP, which is why I suggested that. It may, or may not help, depending on the player.
AC3 is the DVD spec for audio. Although most players can handle mp2 and lpcm, not all can play it properly. Generally, if the player can also play mp3's, then mp2 seems to be OK.
Get Ffmpeggui and use it to transcode all audio to 48khz 224kbps AC3. Import the AC3 into dvdlab, instead of the mp2. Tmpgenc is notorious for spitting out crappy audio, after all, it IS a video encoder. Audio isnt' it's forte. Even ffmpeggui's AC3 can be problematic. Make sure you get the latest version. If you have tmpgenc's audio player (buried in the tmpgenc folder, with no shortcut to it), you can use it to transcode to AC3. It does a much better job.
Your media, and method of burning are exactly what I use with no troubles.