a plug above the brake booster has to be grounded and then you set base timing, no vac advance on the 3.0 motor. I would personally triple check the timing marks, even though they looked fine, turn the motor by hand and make sure nothing moved, tension on the belt if not set just right will come back to bite you.

Richard E
1989 Montero - Stock-ish
1989 V6 Auto Raider - 5.3 Vortech Swap.
1987 Mitsubishi Starion 2.6t, soon to be 3.5
1983 Honda XL600R