Sorry to depress you further but 75w90 is really a manual gearbox fluid. Are you talking about your automatic transmission? If so, if it's a petrol model you need Esso LT71141 and for the diesel it's Texaco ETL-7045E. These fluids, though, are difficult enough to get hold of in Europe and the States so goodness knows how easy it will be to source them in Tanzania!
Phil
Phil