Our Old Hyundai Grace (Square lights) Van isn't kicking up very well

Hi Guys,

I am new here, i recently check on some sites and forum sites and I found tsikot.com interesting. My dad owns a very old van (Hyundai Grace Exported). Recently we had it checked by a family mechanic and he suggested an overhaul for the engine since we alway experience overheating engine even if the A/C is off. We did notice a positive change (fuel consumption, engine temp) but i also noticed(recently drove it to Baguio last holiday season) a drastic slow catch up on speed and acceleration. Before we had it overhauled it can flat out up to 125Kph with ease (not overheating) now it can only do around 110Kph plus hill climb on marcos highway is playing between 1st and 2nd (10 pass) gear unlike before we took Kenon road playing only at 3rd and 2nd gear (12 pass mostly adults). What could be the problem? We also recently had the fuel injection checked and calibrated by an expert. I also notice a ticking sound in the engine on idle. I hope somebody can help us.

Thanks!