See if your system is jerky

Weird, whenever I get a spike, it is followed by a sudden dip. In other words, it averages about 16-17, but when it goes over that, then it dips to 0-5 a few frames until it averages back out. Maybe it has something to do with the buffer ahead, except that I get the same thing with both DirectX and OpenGL.
Also, I tried shutting down any backgroup tasks that I could. Now the spikes accur at around 55-60. I think the over 100 spikes were due to some process, but now it seems to be all BlitzMAX.
These modifications to your test program shows that the average remains at 17 regardless of the number and height of the spikes

'SetGraphicsDriver GLMax2DDriver()
Graphics 800,600,32
'Graphics 800,600,0

Local t1:Int
Local t2:Int
Local test: Int
Local high: Int
Local lo:Int = 200
Const MAXVALUES=800
Local values:Int[MAXVALUES]
Local counter=0
Local loops = 0
Local average = 0
Local total = 0

While Not KeyHit(KEY_ESCAPE)
	t1=MilliSecs()
	Cls
	DrawText "Current: "+test,0,0
	DrawText "High:    "+high,0,20
	DrawText "Low:     "+lo,0,40
	DrawText "Average: "+average,0,60
	DrawText "Press <Space> to reset High",0,80
	DrawText "Press <Escape> to exit",0,100
'	DrawText GCMemAlloced(),0,80
	For Local i=0 To MAXVALUES-2
			SetColor 255,255,0
		DrawLine 0,500,600,500
		SetColor 255,255,255
		DrawLine i,500-values[i],(i+1),500-values[i+1]
	Next
    Flip 1	
	t2 = MilliSecs() 
	test:Int = (t2-t1) 
	If test>high Then high = test
	If test<lo Then lo = test
	If KeyHit(KEY_SPACE) 
		high = 0
		lo = 200
		loops = 0
		average = 0
		total = 0
	End If
	values[counter] = test
	Counter:+1
	If counter>=MAXVALUES Then counter = 0
	loops :+ 1
	total :+ test
	average = total/loops
Wend