My 1991 volvo 740 turbo sw has sluggish acceleration, engine revs high before engages and moves forward

Start by checking the automatic transmission fluid level hot. You may want to take this to a local Volvo dealer to have the transmission serviced first.

Usually when the transmission slips, shifts rough, is noisy or has no drive in forward or reverse gears this indicates that the fluid pressure is low. When the transmission is serviced the oil is drained, the screen/filter is changed, the magnets cleaned and the pan cleaned as well. Dirt can clog the screen, which is a filter that is designed to trap particles that would otherwise damage the unit. The magnets are designed to trap metal shavings before they can contaminate the oil.

If this fails to correct the issue, the clutch packs could be worn out inside the transmission itself. These are the friction plates that actually perform shifting duties. The other possibility is that the torque converter or its pump is worn, resulting in low line pressure. Although replacement is possible, consider a rebuilt unit before repairing - the cost of installation of a rebuilt unit is usually about the same for repair of these types of problems. The result will be a vehicle that is both reliable and long lasting.