Mitsubishi Express 2008

I have Mitsubishi Express 2008 manual transmission Van. It’s petrol/lpg. I recently got it serviced (Engine oil, oil filter, coolent, brake fluid, rear axle oil, manual transmission oil, spark plugs, air cleaner filter). After servicing, power/pickup/speed on lpg got reduced however it’s still the same on petrol. Please let me know what went wrong?