These two came to mind but if you are getting noise an internal leak or like procomp said blocked fluid flow may have caused a lack of lubrication and is ruining hard parts now.
Slow, slipping or no reverse “lo-reverse” clutches are worn out, fluid leak in the reverse apply circuit, or broken sunshell.. May also have worn boost valve. It is possible to remedy a fluid problem by removing the checkball from its cage in the case in the rear of the Transmission may help (must remove valvebody), or adding a high-viscosity additive such as Lucas Transmissionmission additive or other seal restorer product.
1-2 shift does not happen at WOT until you let off the gas. Middle case leak in the 2nd gear apply circuit (servo assembly or 1-2 accumulator). Doublecheck by using the pressure gauge and watch for a big drop when the PCM commands 2nd gear. Worst case poor line pressure rise (see below). Try replacing the ThrottlePosition Sensor ThrottlePosition Sensor (TPS).