I find the V8 throttle pots quite reliable, they are probably out of production and why the part you got was so old (I'd be more wary of newer non OEM parts anyway).
One solution might be to dump the EDC system and fit a mechanical pump and injectors. EDC gives about 10bhp more than an untweaked TDi though and IIRC it was introduced onto Auto TDi first to help performance.