Q.Engine oil changed- affects bike performance​

Hi, I have hero Honda CD deluxe. I had changed engine oil from local garage. Person put Shell 20w50 oil and engine started malfunction ing. Now I am noticing poor pick up and getting mileage only 35 km/ltr. Before oil changed, I was getting 60 km/ltr city mileage. I was told to change clutch plates since they were slipping. I changed those as well but no improvement. So I got my bike to Hero service station and told them the bike's history. So they used engine flush to drain previous oil completely and fill the 10w30 oil. Afterwards I noticed the bit improvement. Now I am getting 48 km/ltr. But I am expecting 60 km/ltr as what bike had initially. Please advise the expert solution. Also let me know if Honda 10w30 oil is compatible with Hero Honda CD deluxe.

Regards,
Amit