i have a 2000 expy, 4.6L, 4x4 & i've been getting some detonation when i'm just cruisin at around 40-45 mph and it goes into overdrive. Troyer said 87 octane was fine for a relatively stock engine(k&n fipk, FAL-270).It only has 30K on it! Do I need higher octane or a tune-up or both?

 

You need to try cleaning the MAF. Possibly the throttlebody EGR ports. Check PVC elbow. Clean carbon by using SeaFoam or something equivelent through the pvc or brake booster line.

from the experience I have had with my 5.4 I would then go have the PCM flashed as that is what finally fixed mine pinging that started around 36K.

tom