Surging please help.

[RGuzz]

Hello,
Back behind the wheel of a 200TQ 160k miles TAP chip other mild 
modifiers...current problem is surging very noticeable at steady 3-4k 
RPM's no idle problems. Occurs both cold (here it is constant at all 
RPM's) and at 3-4k steady throttle. 02 sensor just replaced( no 
improvement) new proper plugs, air filter. Haven't run any codes. WG 
spring is TAP and hasn't been adjusted by me. Problem has worsened 
considerably last 2k miles. Full boost is present and car runs great 
under full throttle. Wires, metal gear distributor fairly new. No plugs 
fouled, tailpipes slightly blackened, bouncing speedometer are other 
problems I have noted.
Numerous suspects can account for this from what I gather.
I need a few simple places to start looking to solve this problem. It 
occurs with AC compressor on or off.
Help!  And thanks after 2 years away!
Richard