I have an 1995 S10 Blazer 4x4 4.3L. When the car is cold the transmission seems like it's not grabing or maybe it's slipping? The engine seems to be reving up but the car is not moving as fast as it should. After the car goes about one block it's okay and it does not do it the rest of the day. The transmission has been serviced recently (oil and filter) but not for this problem. Any thoughts