Replace the harmonic balancer pulley, its slipping, that's why your timing mark wonders, in first gear the engine is under its heaviest load, which is getting the car moving, so it has to put out more power. Under that load the inner ring of the begins to turn and the rubber ring around it begins to slip, allowing the outer ring to move out if sync with the crank screwing up your valve timing by (I believe) retarding it. Install this guy http://www.ipdusa.com/products/5645/106261-crankshaft-harmonic-balancer-damper-pulley
set your timing and then go for a drive, all should be repaired
If the link didn't work here's the IPD part number and name
106261 - Crankshaft Harmonic Balancer (Damper) Pulley
Let me know if this fixed it, best of luck
~Naturally aspirated 92 Volvo 240 Wagon