Car does not turn over while on a slope

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The abs and engine lights are always on. When I park in drive-way with a little slope downward it will try to kick over but doesn't. This happens occasionally. Battery is new, plugs new, plug wires new, plenty of high octane gas. If I let it rest for 3-5 minutes while the engine is still cold it will then turn over. When parked in the garage or at work on level ground it kicks over every time. I have 237,000 on it...