over heating

hy !
i got a 1995 sportage mr .. and i recently discovered that i have problems in the head of the engine. the head itself is cracked ... i got loss of power , water consume , oil consume ... i talked with a mecanic , and he said that heads of enginefrom kia had heating problems , that the motor itself were bad designed , and put to much pressure on the head .. and if i buy another one new , soon or later i will get the same problem .. he advised me to buy one that wasnt from kia and it was suitable for sportage ( more cheaper by the way ) .

is this true ?

if it is , is the engine from sportage year 2000 with this problem also ?

i also got a problem , that when i reach like 120-140 km/h or i need to give some gas to sportage , i look behind , and its like a cloud of black smoke .. could this had anything to do with my motor problem , or is something else ?

could someone if had problems like this , how they overcome it ? do i need to change something in the vehicule , some parts , or whatever to give better performance and less engine problems ...

i like my sportage , but sometimes , it just gives me a headache :(