You probably have a vacuum leak somewhere along your hoses leading to your intake manifold. Since the car doesn't move fast, it won't shift gears. The vacuum leak will cause your car to run very rich when the turbo should be engaged. This is because the air mass meter sees an large intake of air when the turbo kicks in and orders more gas to the cylinders. The air ends up leaving through the air leak some where and the fuel burns up rich.
Check for a leak in a critical area such as the hose leading to and away from the intercooler.
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-Brandon at FSU '88 744ti 150k miles