Are you absolutely definite the shift problem is not actually a very heavy misfire, I have one when it's been raining and the car shudders heavily. At first I thought it was a transmission problem, although it only happened under load and at low revs. I haven't got round to doing plugs and leads yet.
2.5-16v 1990 90,000m Astral Silver
2.0E 8v 1986 107,000m Black